Sen. Thom Tillis, a North Carolina Republican who has been criticized by the right for at times parting ways with President Trump, has drawn a primary challenger in his 2020 reelection race.

Garland S. Tucker III, chief executive of a Raleigh investment company, filed paperwork Monday with the Federal Election Commission to run against Tillis in the Republican Senate primary. News of Tucker’s move was first reported by the Raleigh News & Observer.

Tucker is an “old-fashioned conservative” on issues such as federal spending and national defense, said his campaign adviser Carter Wrenn. “And he looks at where Tillis stands on those issues, and he disagrees with him,” Wrenn said.

Tillis’s campaign fired back with a statement suggesting that Tucker is an “anti-Trump activist.”

Tillis, North Carolina’s former state House speaker, ousted incumbent Sen. Kay Hagan (D) to win election to the Senate in 2014. During that year’s Republican primary, Tillis bested several tea party challengers to win the nomination, in what was viewed as a major victory for the GOP’s establishment wing.

In the two years since Trump took office, however, Tillis has drawn scorn from some of the president’s supporters for opposing parts of his agenda.

As the White House and congressional Democrats sparred in February over funding for Trump’s long-promised border wall, Tillis wrote a Washington Post op-ed announcing that he would vote in favor of a resolution disapproving of Trump’s declaration of a national emergency on the issue.

“It’s never a tough vote for me when I’m standing on principle,” Tillis said in an interview with The Post defending his decision.

But then, when the day of the vote came, Tillis reversed course and voted against the resolution, citing his conversations with Vice President Pence and other Republicans as influencing his decision to side with Trump.

Tucker’s campaign on Monday accused Tillis of having “flip-flopped” on the issue and pointed to the reversal — as well as Tillis’s opposition to Trump’s proposed cuts to foreign aid — as an example of differences between the two candidates.

“Running against an incumbent is an uphill climb, but Tillis is a surprisingly vulnerable incumbent,” Wrenn said.

Monday’s filing of campaign paperwork is Tucker’s first step toward running; he plans to make a formal statement in the coming days, Wrenn said.

Tillis’s campaign manager, Luke Blanchat, said the senator is “no stranger to primaries and he is fully prepared for another.”

“He looks forward to defending President Trump and his policies against any anti-Trump activist who chooses to enter the race,” Blanchat said in a statement that made no mention of Tucker by name. “Senator Tillis looks forward to continuing to work with President Trump and Vice President Pence in securing our border and keeping our economy growing at a record setting pace.”

Tillis’s team pointed to a 2016 News & Observer column in which Tucker said he was begrudgingly voting for Trump, whose nomination he had “stoutly resisted” during the primary.

“Trump is a twice-divorced, self-acknowledged adulterer who has, in the course of this campaign, uttered some of the most unkind, disgusting comments ever made by any American politician,” Tucker wrote in the piece. “Sadly, Clinton offers no personal moral superiority.”

In May 2015, Tucker hosted a 250-person luncheon in his backyard for then-Wisconsin Gov. Scott Walker’s campaign for the Republican presidential nod.

Among the Democrats who have announced bids for Tillis’s seat are state Sen. Erica Smith and Mecklenburg County Commissioner Trevor Fuller.

Even before Tucker jumped into the race, a primary challenge against Tillis had been widely expected.

The National Republican Senatorial Committee, Senate Republicans’ campaign arm, defended Tillis on Monday. Tillis has served as the committee’s vice chairman.

“Senator Tillis has been a strong conservative fighter for North Carolina,” NRSC Press Secretary Joanna Rodriguez said in a statement. “This will prove to be nothing more than a quixotic adventure for a wealthy, out-of-touch liberal who was talked into this by a past-his-prime political consultant looking for a paycheck.”

Rep. Mark Meadows (R-N.C.), a close ally of Trump, said in an interview with The Post last week that while he personally has no plans to challenge Tillis, he expected that the senator “will have a legitimate primary opponent.”

Meadows also said he “fully expects” Tillis to win reelection — but notably declined to throw his support behind him.

“He’s not asked me for one,” Meadows said when asked about the possibility of an endorsement. “I doubt that I would give a congressional endorsement to any senator, that it would matter.”

Aaron Blake contributed to this report.