Where does an insurgent conservative go to launch a primary challenge, win credibility with the Trump base, and maybe even attract the attention of the president? The Sean Hannity radio show, of course.

On-air last Wednesday, Garland S. Tucker III announced his plans to enter the Republican Senate primary in North Carolina. “Sen. [Thom] Tillis is going to love me for this interview,” Hannity said dryly before giving the Raleigh challenger his endorsement.

“My attitude is very, very simple: Whoever is going to be the guy that goes in, rolls up their sleeves, and fights for their promises, and the president’s agenda, which I have advocated 30 years on air, I’m for,” Hannity told his 15 million weekly listeners.

Tucker told RealClearPolitics two days later he hoped Trump was tuned in.

The president has not said anything publicly and two outside advisers told RealClearPolitics they didn’t even know of Tucker before his Hannity appearance. But the emerging story offers something of a twist: A former Trump skeptic attacks an incumbent Republican over his lack of allegiance to the president; a primary becomes another loyalty test.

Tillis introduced legislation to protect Special Counsel Robert Mueller, bucked Trump to keep foreign aid flowing that the president wanted to curtail, and wrote an op-ed in the Washington Post condemning Trump’s decision to declare a national emergency to build his border wall. He then reversed course and voted to support that last move, but not before taking fire from the right.

“My view is that if Tillis is a friend,” Tucker told RCP, “well, if you have friends like that then you don’t really need enemies.”

Republicans are taking the challenge seriously. Vice President Mike Pence will be dispatched to North Carolina next week to help the incumbent patch things up with grassroots voters. The National Republican Senatorial Committee rallied behind him too. And Tillis jolted his campaign to life, telling staffers that “it’s time to get cracking.”

The establishment strategy, so far, has been to dismiss Tucker as a wealthy retired businessman making an unwelcome political foray after voicing hesitation about Trump in 2016.

“This primary is nothing more than an opponent of the president’s agenda with money to burn teaming up with a past-his-prime political consultant who is desperate to cash a paycheck,” NRSC spokeswoman Joanna Rodriguez told RCP.

A longtime Republican donor, Tucker finds this ideological labeling puzzling. One Tillis ally called him “an anti-Trump activist.” He said another dismissed him as “an out of touch liberal.” Neither, he insists, is accurate: “Old fashioned conservative is a better fit for me.”

And Tucker really does sound old-fashioned. He talks debt and deficits, warns of high taxes and ballooning budgets, praises less government and more freedom. It is the sort of Tea Party rhetoric that helped Republicans retake the Senate back when grassroots voters still dressed up like minutemen. Tucker backed that movement, and he later cut two $2,600 checks to the Tillis campaign.

When conservatives began trading tri-cornered hats for red MAGA caps, however, Tucker started getting nervous. He backed Wisconsin Gov. Scott Walker, then Florida Sen. Marco Rubio and later Texas Sen. Ted Cruz in the 2016 GOP presidential primary. After all three of those campaigns ended, he even backed Ohio Gov. John Kasich briefly. Only after the Republican National Convention in Cleveland, when every other option was exhausted, did Tucker reluctantly board the Trump train.

“My conscience is clear,” he wrote in 2016 in an op-ed for the Raleigh News & Observer. “I am in no way responsible for Trump as the nominee.”

What followed was somewhat typical of the time. The GOP was soul searching and Tucker, like others, was coming to grips with how a thrice-divorced philander who shamelessly cheated on his wives and bragged about dodging taxes could become the standard-bearer of the party of social and fiscal conservatism. Contrary to what his current critics say, though, Tucker was not Never Trump. He voted for him. He urged Republicans to do the same.

“It never feels very good to arrive at a decision via negative reasoning, but it’s far easier for me to commit never to vote for Clinton — and the 2016 Democratic platform — than it is to commit to vote for Trump,” he wrote in the op-ed.

Almost three years later, Tucker is relieved to have been wrong. Pointing to confirmed judges and tax reductions, he said Trump’s conservative record has been “the wonderful surprise of this presidency.”

The newly minted candidate, who has a byline at National Review and a well-respected book on American conservatism (Amity Shlaes wrote the forward), now places Trump in the political pantheon of limited-government types.

“I would say that with Trump, the most important way to look at him is his policies,” he said. “Those are right out of the Reagan-Thatcher playbook. There is a lot of noise and Trump’s personality is certainly different than anyone we have ever seen, but I think his policies have been amazingly consistent.”

Also consistent: Tillis. According to an analysis published by FiveThirtyEight, the first-term senator has voted with the president 95% of the time. Tucker agrees with Tillis on major issues like abortion and judicial confirmations and tax cuts. But the former Tillis supporter said the incumbent has gotten too comfortable on Capitol Hill.

Tucker told Hannity that his opponent is like other Republicans who have discovered that D.C. is more sauna than swamp. They get to Washington “and they sit down in the hot tub and start enjoying it. I think that’s what has happened to Sen. Tillis.”

For proof, he points to the Tillis flip-flop on Trump’s national emergency declaration and notes legislation he co-sponsored to put 1.8 million DACA recipients on a pathway to citizenship.

“We cannot grant a path to citizenship for anyone who came here illegally,” Tucker said before adding that he would likely support the immigration plan authored by the president’s son-in-law, Jared Kushner, and reportedly making the rounds in Congress.

Tucker may want a wall but he is hardly a carbon copy of Trump. He backs “some sort of amnesty,” condemns mass deportation as impractical, and wants to see an increase in legal immigration.

What is untenable, Tucker said -- borrowing a line from the late economist Milton Friedman -- is an open border with a generous welfare system. And he wants deep cuts to domestic spending.

Tucker sees a little bit of Calvin Coolidge, the last president to leave the federal government smaller than he found it, in Trump, the only president to have owed billions of dollars to creditors. He doesn’t fault him for the federal debt and notes the proposed spending reductions buried deep inside the president’s record-breaking $4.75 trillion budget. The blame, he said, belongs to Congress:

“I really think that Democrats as well Republicans, when they are honest with themselves, look at our spending and say, ‘Gee, this cannot go on forever,’ and they are right. It can’t. We need to make some tough decisions and they won’t be easy, but that’s what we need to do.”

But Democrats are not taking budget cuts seriously, and Republicans have forgotten their Obama-era talking points about fiscal responsibility. What’s more, Tucker talks about federal balance sheets in terms of ethical obligations to the next generation. It is, he said, “a morality question.”

The challenger knows that the primary will be a referendum on presidential loyalty. And he is so dissatisfied with the tenure of Tillis that he is willing to self-fund a large portion of his campaign. He is not, however, willing to paper over his past criticism of Trump. Tucker still regards the personal life of the president as “not exemplary.” But the candidate also hopes that the race will become a throwback to old-school conservatism, the kind that once helped Republicans capture the House and the Senate. He seems suited to that kind of race.