(Revised at 2:03 pm ET with new Ron Paul-Pennsylvania material.)

The contest for the Republican presidential nomination may be over for all practical purposes, with Mitt Romney the all-but-certain GOP nominee. But that doesn't mean there's nothing of interest in Tuesday's primaries.

Voters are going to polls in Pennsylvania, Rhode Island, Connecticut, Delaware and New York, though turnout is expected to be low. Still, here are four things to watch for.

Does Romney win everywhere? — With Rick Santorum, who had been his most formidable remaining rival, exiting the race recently, Romney is expected to do well in the New England and Mid-Atlantic states holding primaries Tuesday.

In contrast to Romney who's only made one appearance in the state in the runup to Tuesday's primary, Newt Gingrich has spent a lot of time campaigning in Delaware as though he expects it's possible to pull off an upset there in what is being viewed as his last chance to make a statement.

Gingrich, whose campaign has bumped along bottom for weeks, has even received some late endorsements from members of Delaware's GOP leadership. A report in the Wilmington News-Journal suggests the former U.S. House speaker has benefited from merely showing voters in the small, often overlooked state some attention.

But the same report also indicates that Republicans in the state, like many elsewhere, are ready to move past the primaries and into the general election. If those voters come out in high enough numbers, it could spell the end of Gingrich's last chance to steal any of Romney's spotlight.

Can Romney reach 50 percent or more everywhere? — In terms of state primaries, Romney exceeded 50 percent in Massachusetts and Virginia and came ever so close to that mark in Maryland, coming in at 49 percent.

He reached 86 percent of Republican primary voters in Puerto Rico and 70 percent in Washington, DC which, of course, aren't states.

That was all before Santorum exited the race and left the field open to Romney. So it should now be relatively easy for Romney to exceed the 50 percent threshold everywhere Tuesday evening. If he doesn't, that would, if nothing else, give pundits one more thing to pontificate about.

Does Ron Paul do something unexpected in Pennsylvania? — Josh Putnam, a political scientist and visiting professor at Davidson College in North Carolina and keeper of the Frontloading HQ blog, one of the best guides to the primaries, says Pennsylvania is the most interesting of all the states holding primaries Tuesday.

That's because in Pennsylvania voters can vote directly for delegates on the ballot.

In a "low-competition, low-turnout" election like Tuesday's, Paul's supporters could theoretically skew the results more in their candidate's favor by knowing the names of the delegates pledged to Ron Paul and then going to their polling place and voting for those delegates. In an interview, Putnam said:

"A simple Google search will yield you a list of Ron Paul delegates who are on the ballot today. But any similar search for Mitt Romney delegates gets you nothing."I'm not suggesting that the Ron Paul folks will be able to win the delegates or anything like that. But it, to me, bears watching, that in a low-turnout environment that certainly bodes well for either side of this."We've got a nice test case of kind of the traditional name-recognition aspect of this. But we've also got a neat, fervent following, organized sort of side of this as well. That the Ron Paul folks may be able to peel off a few more delegates despite the fact that Romney may win a significant portion of the vote tonight. That delegate vote is more important."

Putnam writes about this situation in a new blog post. It looks like the Romney people, for all of their vaunted organization, may have missed a trick, at least in Pennsylvania.

Romney still has a overwhelming lead in pledged delegates over Paul — 550 to 34 by our NPR count. Pennsylvania has a total of 72 delegates.

What happens in Pennsylvania's new 12th Congressional District? — Before Santorum dropped out, the big question was would he win his home state?

Now, the most interesting race is a congressional contest. Because of redistricting, two sitting Democratic congressmen are pitted against each other — Rep. Jason Altmire and Rep. Mark Critz.

Critz came to Congress when he filled the vacancy left by his late boss Rep. John Murtha in February 2010. Altmire is a three-term congressman.

Critz has the support of organized labor even though he says that if he had been in Congress at the time, he would have voted against the Affordable Care Act which unions supported. Altmire actually did vote against the law.

In a report in the Pittsburgh Post-Gazette, Altmire told us what to watch for:

"You'll be able to tell on election night if turnout is uniform across the district, relatively the same, that's good for me," Mr. Altmire said Monday. "Obviously if turnout is higher in Johnstown than in other parts of the district, that's good for Mark."Copyright 2016 NPR. To see more, visit http://www.npr.org/.