Over the past several weeks, Donald Trump has managed to deliver several scripted speeches that stayed on message. He’s hired top staffers to bulk up his skeletal campaign. And he’s kick-started a fundraising operation, while focusing most of his rhetorical fire on Hillary Clinton.

He can do all that and more, but it still won’t be enough to win Mike Lee’s support.

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“There’s nothing about him running a more traditional campaign that makes me more comfortable because that’s not what I’m advocating. What I’m advocating is a very nontraditional campaign, one that would focus on what I think is the real problem,” the Utah senator said in an interview this week, referring to the erosion of separation of powers and federalism of the United States.

Lee, along with a crew of mostly younger Senate Republicans not facing competitive reelection races, seems increasingly inclined to join Nebraska Sen. Ben Sasse’s “never Trump” caucus, given how much Trump diverges from Lee’s ideal vision of the party’s nominee. With Utah turning against the GOP’s presumptive nominee, and many of Trump’s policy proposals violating Lee’s rock-ribbed conservative core, he’s feeling little pressure to ever get on board the Trump train.

While Republican leaders are cautiously encouraged by Trump’s more predictable campaigning style of late, lawmakers who have long been skeptical of his campaign are unmoved by his tactical changes. Some Republican senators still aren’t even acknowledging that he has their party’s nomination locked up.

“Whoever’s our candidate, I’m going to support our candidate,” said Sen. James Lankford of Oklahoma, a 48-year-old conservative. “I’ll feel better when I get a list of policies and I see who the vice president is.”

“I’m still evaluating,” said moderate Maine Sen. Susan Collins, as Trump stumped in her home state on Wednesday.

It’s not just die-hard conservatives or centrists: Republicans from across the spectrum remain unconvinced by Trump’s course adjustments. For many rank-and-file members, whatever improvements Trump manages haven’t made up for a year of headline-grabbing gaffes, from his initial call to ban Muslims from entering the U.S. to remarks disparaging an American judge of Mexican descent.

“Today, I’m opposed to his campaign,” said Sen. Dean Heller of Nevada. “He did a lot of damage. It’s very difficult for him, as far as I’m concerned, to recover from his previous comments. I’ll give him a chance, but at this point, I have no intentions of voting for him.”

Heller may be looking beyond 2016 to 2018, when he is up for reelection in a state that will be one of the few pickup opportunities for Democrats. Supporting Trump now offers little to no upside to him; but for Rep. Joe Heck (R-Nev.), it’s a must. Heck is running for the Senate this year — and he cannot win without Trump supporters backing him.

Still, most senators up for reelection are hedging their bets in case Trump’s support nosedives — and Illinois Sen. Mark Kirk is outright opposed to Trump’s candidacy. Sen. Pat Toomey of Pennsylvania, who has left the door open to opposing Trump, declined twice on Wednesday to discuss Trump’s new campaigning style and said he wasn’t focused on Trump — even though Trump gave a speech in Pennsylvania on Tuesday trashing new trade deals.

Even senators who’ve announced some level of support for Trump, such as Wisconsin’s Ron Johnson, New Hampshire’s Kelly Ayotte and Florida’s Marco Rubio, have gone to great lengths to emphasize their differences with him, not similarities.

“It’s clear they’ve increasingly professionalized their operation and they’re gearing toward the sort of things you need to do mechanically to be successful in a general election,” Rubio said. “I’ve always viewed my race as separate and distinct. I’m a well-known political entity in Florida. People know my identity, what I stand for. They know what our differences are.”

The less Trump makes inflammatory headlines, the fewer questions senators up for reelection have to face, which is part of what has made GOP leaders slightly more upbeat. But despite the dominant effect that the top of the ticket is likely to have on Senate races, GOP strategists insist that the half-dozen incumbent senators in tough reelection races will win or lose independent of Trump.

“It’ll be helpful to him. But our candidates are going to win on their own,” said Sen. Roger Wicker of Mississippi, chairman of the GOP’s campaign arm. “I’m not seeing much of a coattail or a reverse coattail effect at the top of the ticket.”

Still, GOP leaders are feeling a bit more bullish on Trump’s campaign after a nadir earlier in June, when his attacks on District Judge Gonzalo Curiel drew charges of racism from his own party. Senate Majority Whip John Cornyn (R-Texas) broke his self-imposed ban on Trump talk Wednesday to concede that Trump is doing “better.”

And after weeks of prodding Trump to get away from his undisciplined style, Senate Majority Leader Mitch McConnell (R-Ky.) told TV station NY1 that Trump is getting “closer” to becoming a credible candidate — though he isn’t there yet.

“I’m encouraged by some of the actions he’s taken of late. I do think a little bit more disciplined approach, on message is good,” said Sen. John Thune of South Dakota, the GOP’s conference chairman. “But, theirs is a different campaign; they’re going to run it their way.”

Sen. Jeff Sessions of Alabama, Trump’s original Senate backer, said he’s had several colleagues relay compliments about Trump’s more targeted messaging style and said that Trump is “feeling more comfortable using the Teleprompter.”

“It certainly produced more positive feedback from Senate members that I’m running into. They like the speeches, they think they’re well crafted,” Sessions said. “I would assume the good feedback he’s getting would encourage him to do more of that.”

Despite those encouraging noises, it’s still difficult to find anyone who’s changed their mind about Trump even after he fired his divisive former campaign manager Corey Lewandowski. And Trump is still making Republicans wince, whether it’s his attacks on Sen. Elizabeth Warren (D-Mass.) as “Pocahontas” or declaring new trade deals as a “rape” of the United States.

Sen. Jeff Flake (R-Ariz.), another senator up for reelection in 2018 in a heavily Latino state, has been openly begging for Trump to give him and other distressed Republicans a reason to join his campaign. But he called Trump’s attacks on trade deals “very, very bothersome and very damaging.”

“It’s only been a couple of days. He’s shown those signs before and just snapped right back to the old Donald. So it’s a little too early to tell,” Flake said.

Yet rather than specific policy differences with individual senators — which is expected between a nominee and rank-and-file lawmakers — Lee’s concerns go even deeper: a fundamental difference over the balance of power between Congress and the executive branch, a subject Lee has written about in his book,“Our Lost Constitution.” As Lee promotes the release of a paperback version, he finds himself relating the entire point of the book in the context of Trump — and why Lee can’t support him.

“I wonder if there isn’t somebody lurking within him who really wants to leap out and promote federalism and separation of powers and talk about how he’s going to reform Washington,” Lee said a bit wistfully. “He hasn’t done that. And I haven’t endorsed him.”