Rand Paul is back to doing what he does best: Trolling his fellow Republicans.

And this time, his party might thank him for it.

More than Jeb Bush, the establishment pick seen widely as the adult in the room; more than Hillary Clinton, the presumptive Democratic nominee who’s taken aim at Republicans; it’s Paul who has arisen over the past week as Donald Trump’s main antagonist, slamming him on the airwaves, in stump speeches and caustic statements from advisers.

“Donald Trump is showing he isn’t suited to lead the country, and I think we all need to discuss why,” Paul wrote in an op-ed for IJReview.com this week that tagged Trump a “fake conservative.”

On Wednesday, the Paul campaign launched a new ad running in Iowa and New Hampshire through the weekend illustrating that point. The ad contrasts clips of his past praise for Democrats and Hillary Clinton — he called her “a terrific woman” who “does a good job” in a 2012 appearance on Fox News — with clips of Paul pledging on the stump to stand up for the Constitution and conservative principles.

And on the trail on Wednesday night, Paul ratcheted up the ridicule, treating supporters at an event in Nashua, N.H. to a colorful impression of the real estate mogul.

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“My favorite is, you know the reason I tell woman they’re ugly, is cause I’m so good looking! Everybody knows I’m good looking, right?” he said, while the crowd erupted in laughter.

Trump fired back against Paul’s ad, saying in a statement that his positions have “evolved” since he backed Democrats and that he “trounced” Paul in a recent game of golf.

“Senator Paul has no chance of wining the nomination and the people of Kentucky should not allow him the privilege of remaining their Senator,” Trump said.

Those remarks drew a sharp response from Paul Campaign Adviser Doug Stafford, who again charged that Trump has no conservative credentials to run on.

“Donald Trump couldn't set the intellectual conservative agenda of anything, not even the tiniest rooms, never mind a country. He is devoid of ideas other than he likes the idea of power and getting attention for foolish statements and bluster,” Stafford said in an email to the Washington Post.

Paul’s flexing familiar muscles with his latest feud — he’s never been one to shy away from a public, and occasionally nasty, fight with another Republican. In 2013 he infamously called New Jersey Gov. Chris Christie the “king of bacon,” a remark that was widely seen as a double entendre meant to reference the governor’s weight as well as his state budget.

Since their initial dustup, the Paul-Christie feud periodically reignited in primetime television interviews, most recently coming to a head on the debate stage last week. There, during a heated exchange over government surveillance, Paul referenced Christie’s now-infamous embrace of President Obama after Hurricane Katrina and then rolled his eyes as Christie referenced his hugs for families after the September 11th attacks.

Paul’s also feuded with Arizona Sen. John McCain, at one point calling him a “lapdog for Obama.” He's knocked Rick Perry’s glasses in an attack on his foreign policy positions, and once shushed a female newscaster in a tense interview that raised questions about his at times prickly temperament.

But with Trump sitting stubbornly at the top of the GOP primary field in polling, Paul’s combativeness could win him plaudits with the party this time around. Republican leaders have been handling the billionaire with kid gloves, worried that he’ll make good on his threat to run as a third-party candidate if they alienate him too much, but Paul isn’t beholden to such concerns.

And there are some benefits to Paul in taking aim at Trump — his new focus has shifted the discussion surrounding his campaign away from reports of disorder behind the scenes, and it’s won him attention from the media as he’s struggled to gain traction in the polls. The most recent NBC/WSJ survey found him squarely in the middle of the GOP field with just 6 percent support.

Still, others in the party before Paul have targeted Trump and seen little if any benefit from it. Both Sen. Lindsey Graham and Perry attacked Trump's credentials and message in the weeks leading up to the debate, with Graham calling the businessman a "jackass" after Trump dismissed McCain's military service. Neither has seen a bump in the polls, and both remain at the bottom of the pack.

But Paul years of practice sparring with other Republicans provides Trump with, at the very least, a more practiced adversary — one who's shown an ability to keep flame wars going over years.

And while his feuds have earned him a reputation as a bit of a bully in the past, Paul may have found a way to turn that reputation into an asset: Challenge an even bigger bully to a duel.

“If no one stands up to a bully, a bully’s gonna keep doing what they're doing,” Paul said during a conference call on Trump with reporters this week. “Unless someone points out that emperor has no clothes, they’ll continue to strut about, and what we’ll end up with is a reality TV star as nominee, if we’re not careful.”