Massachusetts Republican Geoff Diehl of Whitman, a 49-year-old father of two and a four-term state representative, is trying to unseat one of the nation’s best-known senators before she can mount a challenge to President Donald Trump in 2020. To beat Elizabeth Warren, Diehl is walking a fine line, tapping into the distaste some voters feel for Warren while maximizing his Trumpian pedigree with the faithful.

Diehl has spent most days on the trail aboard his mobile campaign headquarters, an RV sporting hyper-sized photos of his scout-master-with-a-mission profile. On a recent Saturday in September, he rolls into Gardner, Massachusetts for the annual Oktoberfest event. My advance research suggested it would be an essentially Trump friendly crowd, pulling from red, blue and purple communities -- with enough undecided voters to allow the candidate can make an impression.

“You’ve got my vote, believe me. Anyone but her,” Joe Burns, a retired attorney, said to Diehl upon meeting him at the table near the beer tent. Like a lot of conservative voters in suburban Massachusetts Diehl encounters, Burns would be thrilled to see Warren’s political star extinguished.

“I think she’s a disgrace — an embarrassment to democracy,” Burns told WGBH News. “I think that this guy can get the job done.”

Diehl's mobile campaign headquarters winds through Sudbury, Massachusetts on a recent weekend.
Meredith Nierman WGBH News

This is the essence of Diehl-Warren contest — unvarnished polarization, with a focus on the “job” of the state’s U.S. Senator. Democrats want Warren to fight Trump any chance she gets, often by whatever means she can. Republicans would rather the congressional delegation focus on delivering funds for the state, and that means cooperating with Trump and the GOP majority.

Massachusetts may be a blue state, but like America at large, political differences run deep. In the 2016 presidential primary Donald Trump got more than one million votes. Diehl’s challenge is to stretch that margin, and his campaign ads illuminate the strategy.

“I’m Geoff Diehl, the guy who stopped automatic gas tax hikes, and now I’m out to stop partisan gridlock in Washington,” Diehl introduces himself in his first major campaign commercial.

On that first part, Diehl was a leader two years ago in the ballot campaign that reversed the Legislature’s decision to index the gas tax to inflation. Fifty-three percent of voters opted to save money rather than spend on transportation.

“Beacon Hill was going to just have it automatically go up,” Diehl said in between campaign stops aboard the Fleetwood RV. “There was no accountability of where the money was being spent, so I thought that that was the wrong way to go.”

As for the second claim, Diehl is about as conservative as Warren is liberal. Anti-tax groups give him high marks, the local NRA affiliate rates him A-plus, and Planned Parenthood considers him an opponent of abortion access.

There is little in his State House record to suggest Diehl would be anything other than a Trump Republican should he go to Washington. Diehl would help end partisan gridlock in Washington only because he would strengthen the Republican hold on the Senate.

His State House GOP colleague, Rep. Peter Durant from Spencer, said the state’s all-Democratic delegation needs someone who lines up with Trump.

“I think Geoff can bring things back to the state,” Durant said. “That’s what we need. Somebody who can actually work with the administration as much as all the rest of the delegation despises this man. So, I think that’s important.”

On the campaign trail in Sudbury, Diehl stops to talk to a constituent.
Meredith Nierman WGBH News

On Beacon Hill, Diehl is a reliable Republican vote against the Democratic majority. It’s hard to generalize beyond that. He has been the primary sponsor of 59 pieces of legislation since his election in 2010. Only two of those bills passed the Democrat-controlled Legislature. It’s not a record that impresses fellow legislators of either party.

But back home in his district, Diehl has a reputation of being accessible and fighting for schools. Daniel Salvucci, the vice chair of the Whitman select board says Diehl worked with a Democrat from neighboring Hanson to increase funds for the towns’ regional school district.

“Geoff is of course a Republican, but he crossed the aisle, they both got together and ... [were] able to increase the funding for each student which helped out the towns of Whitman and Hanson,” Salvucci said. “It’s one of our biggest expenses for our town, and this is where we need the help.”

If the implicit message of the Diehl campaign is Trump’s the guy, the explicit message is that Warren isn’t focused on Massachusetts. Diehl’s TV ads say Warren should resign if she’s considering running for president.

“One of the things is just focus on working for Massachusetts rather than trying to use the office for a springboard for something else,” Diehl said.

Diehl himself, of course, has been on the campaign trail far from his South Shore base almost non-stop in recent years. There was the 2014 gas tax battle. Then his unsuccessful run for a Brockton State Senate seat. After that, he helped Trump win the Massachusetts GOP presidential primary. And now he’s sowing Trump-style conservatism from his Fleetwood RV.

“It should purely be about your record, decisions you’ve made in office and how it affects the people of Massachusetts, and that’s why it’s important to keep the conversation civil and focused on what we can do to move our county and our state forward,” Diehl said.

To those voters who are less-than-enchanted with Warren, Diehl’s argument is a siren song. He is staking his political future on the proposition that he can convince middle-of-the-road voters to overlook most of his conservative positions and send him to the Senate to replace that White House-dreaming Elizabeth Warren because he’s a hometown sort of guy.

Clarification: A previous version of this story described the crowd at the Gardner Oktoberfest as “Trump friendly,” based on reporting and Gardner’s and surrounding towns’ voting histories. The Diehl campaign did not characterize the event in any partisan manner.