Almost two years ago, in the Senate’s second vote of the 114th session, Senators Elizabeth Warren of Massachusetts and Bernie Sanders of Vermont voted against a bill helping business get insurance against terrorism. The other 10 Senators from the six New England states were willing to swallow a provision, added by Republicans, altering the Dodd-Frank financial regulations. Warren and Sanders said no.

The same two stood apart from the others again, nearly two years and 500 votes later. This time, it was the 21st Century Cures Act, and the poison pill was giveaways to the pharmaceutical industry.

As these two examples show, senators vote differently from one another not only because of ideological differences but also based on their strategic and temperamental approaches to legislating.

Call it obstinacy or call it principled independence, but that trait of Sanders and Warren stood out as I analyzed the votes of all 12 New England senators in the just-finished law-making session.

This is the season when news outlets and advocacy groups seek to pin ideological labels on lawmakers. Inevitably, those efforts are skewed, especially when viewed through the prism of special interest groups.

Even a seemingly straight "yes" or "no" vote on a given piece of legislation is rarely cut and dry. What comes to a vote is not a reflection of national priorities but a sampling of what leadership wants. In the Senate, that means Republican Majority Leader Mitch McConnell of Kentucky sets the agenda.

It's true that significant final votes, like the two cited above, are obviously more important than others. But grading systems that pare down to the most consequential votes can miss some that are technically procedural but still reflect underlying ideology — such as “motion to proceed” votes that stop a bill from coming to a vote. Those tightly focused vote ratings can also leave out symbolic but telling no-hope amendments, like when Democrats forced votes on acknowledging the importance of climate change.

Still, though the opaque process resists clean numeric representation, analyzing two years of Senate votes tells an interesting story about the differences among U.S. senators representing New England.

New England's congressional delegations lack the hard-right conservative Republicans who dominate Washington politics, but the group is hardly homogenous.

It includes two Republicans — one, Kelly Ayotte of New Hampshire, now voted out of office — along with eight Democrats from the six states in the region, each with a unique set of priorities and a different approach to legislating. There are also two independents who caucus with the Democrats: Angus King of Maine (a moderate) and Sanders (a self-defined democratic socialist).

In the big picture, there was naturally a considerable amount of agreement. In 76 percent of all roll call votes, all the Democrats and independents voted the same way. Perhaps more surprising, in a full 42 percent of the total, the entire New England delegation voted together, with both Ayotte and Maine’s moderate Republican Sen. Susan Collins joining the Democrats.

Many of those were unanimous or near-unanimous bi-partisan votes on uncontroversial confirmations or easily agreed-to items.

But Ayotte and Collins often split from more conservative Republicans. They split away on quite a few amendments by their party’s extremists, but also on some offered by Democrats attempting to recognize environmental threats, favoring rights for same-sex partners, and helping opioid addicts — a pressing bipartisan issue in New England.

Particularly on amendment votes requiring 51 “ayes” for passage, those two Republicans' willingness to join the 46 members of the Democratic caucus was not decisive, but it was certainly not insignificant. Their votes helped add a resolution in favor of federal benefits for legally-married same-sex couples to the Senate budget bill, on a close 52-48 vote, in March 2015. During that same budget amendment process, they pushed a mostly symbolic vote favoring paid sick leave just over the 60-vote filibuster-proof total — sending the signal that such a law would pass if McConnell ever allowed it to come to the floor as a bill of its own.

That sick leave amendment was one of 29 “key votes,” out of 42 tracked by the Heritage Foundation during the two-year session, on which Republicans Ayotte and Collins voted together against the conservative position.

But when the two split with each other, it was far more often Collins than Ayotte joining the New England Democrats — three times as often, by my count. Those votes, often on relatively minor provisions, reflected Ayotte’s more right-wing positions. For example, both Republicans ultimately voted in favor of a major education reform bill in 2015. But along the way, they split on four proposed amendments. Notable among them, Ayotte favored allowing states to opt out of federal standards, while Collins joined Democrats in blocking that provision.

Lefty-on-lefty disagreement

The region’s 10 caucusing Democrats, including King and Sanders, were hardly a monolithic group. On just about a quarter of votes during the session, they were split among themselves.

On a purely numeric count, the two very different Independent senators were most and least likely to vote the same way as the New England Republicans. King, a moderate, unsurprisingly was most likely to join Ayotte and Collins on issues. And no surprise that Sanders, campaigning for president as liberals' favorite, joined Ayotte and Collins the least.

In fact, the three New Englanders most likely to stand against Republican votes were Sanders, Warren and Ed Markey — who were also, according to GovTrack’s rankings, the three most liberal senators in the country for the two-year session.

So, yes, ideology had a fair amount to do with voting differences. Aside from King, Jeanne Shaheen of New Hampshire is generally viewed as the most moderate of the Northeast Democrats, and my analysis found her to be most likely to cross the voting line to join Republicans. She was followed, by my count, by Richard Blumenthal of Connecticut, Sheldon Whitehouse of Rhode Island, Chris Murphy of Connecticut, Pat Leahy of Vermont, and Jack Reed of Rhode Island.

But the details of the votes show important differences that didn’t often break cleanly among traditional ideological lines. In many cases the votes reflected different priorities on national security.

Votes on the Cybersecurity Information Sharing Act last October, for example, revealed differences over the balance between security and privacy.

Privacy concerns led Leahy, Markey, Sanders, and Warren to vote against that bill, while the others voted in favor. But only Whitehouse, a former prosecutor who served as U.S. attorney and attorney general in Rhode Island, went so far as to vote for an amendment that would have allowed tech companies to share information with the FBI and Secret Service, in addition to the Department of Defense, without liability. Whitehouse and King — who serves on the Senate Select Committee on Intelligence and the Armed Services Committee — joined Republicans voting against an amendment requiring companies to remove personal information from threat indicators shared for security. Those two, plus Murphy and Shaheen, voted for a similar but narrower amendment. And on an amendment — offered by Leahy — to remove a Freedom of Information Act exemption, it was Markey joining King, Murphy, and Whitehouse to vote no.

On another security versus privacy vote, in 2016, King, Reed, and Whitehouse voted in favor of allowing the FBI to issue “national necurity letters” — administrative subpoenas that don’t require a court order. The other area Democrats helped block that amendment to the SHIELD Law.

On other national security issues, it was West Point grad Reed most often breaking with liberals — usually to preserve compromises he made as ranking member of the Senate Armed Services Committee.

How high your horse

Across a variety of issues, Markey, Sanders, and Warren were most likely to stand on principle, opposing compromise legislation despite favoring much of the bill’s intent.

Because of the addition of what she called “goodies” for the financial industry, Warren was the lone New England dissenter on final passage of a transportation funding bill in late 2015.

Warren was also one of the few, along with Murphy, who refused to vote in favor of the first major education reform since No Child Left Behind in May 2015, citing insufficient accountability for reducing achievement gaps. Both eventually voted yes when the final version came through at the end of that year.

Though Warren gets more coverage for such stands, Markey was just about as likely to vote his own conscience. That won’t surprise anyone who has watched his outspoken nature for decades in the House of Representatives. In one striking instance, Markey voted for passage of this year’s Comprehensive Addiction and Recovery Act only after opposing procedural votes to move the bill forward without additional funding.

Markey, Warren, and Sanders all voted against a bill they argued was insufficient to address Puerto Rico’s debt crisis even though most other Democrats voted for passage.

When Sanders split with his fellow Democrats, it was often over pet issues where he aligns with some libertarian conservatives. He voted to audit the Federal Reserve Ban, and against reauthorization of the Export-Import Bank. Sanders also voted against the USA Freedom Act, along with Republican Sen. Rand Paul of Kentucky, over privacy concerns even though the American Civil Liberties Union praised it for reining in surveillance by intelligence agencies.

On the other end of the scale, Shaheen was more likely to cross her own party by joining Republicans and moderate Democrats, particularly on fiscal issues. Chalk that up, perhaps, to the electorate in New Hampshire, which is far less reliably Democratic-voting that other New England states.

Shaheen was the only area Democrat to vote in favor of fast-tracking trade agreements in 2015. And although New England Democrats usually vote in lockstep with the League of Conservation Voters, Shaheen bucked them to vote yes on a bill on labeling genetically modified foods — even as environmentalists threw money at senators and chanted “Monsanto money” during debate on the bill.

In both cases, Shaheen and Ayotte — the two New Hampshire senators from opposing parties — were the only New England senators voting yes. The two often worked together as a show of moderation politically beneficial to both.

Now, with Maggie Hassan replacing Ayotte, Shaheen figures to have a Granite State voter to her left instead of providing cover on her right. Meanwhile Collins and King, up in Maine, figure to be on the right wing of New Englanders but well left of majority Republicans.

Their votes will become critical in the coming session.

That’s because with just 52 Republicans in the new Senate, McConnell looks poised to circumvent the 60-vote filibuster that will be the only thing preventing him, the GOP-majority House, and President-elect Donald Trump from enacting anything they’d like.

As the Washington Post has reported, Senate Republicans are considering using “budget reconciliation” and other maneuvers to pass a variety of big agenda items with a mere 51-vote majority.

That includes repeal of the Affordable Care Act, tax reform, dismantling much of Dodd-Frank, reversing Obama administration regulations, and even neutering Warren’s Consumer Finance Protection Bureau.

All of this should unite New England’s Democrats in opposition. But it could put Collins and moderates like King in position to dictate the details of some of those bills.