The libertarian-minded Massie has broken with Trump on an array of key issues, which McMurtry has highlighted repeatedly since launching his campaign earlier this month. But Massie’s new commercial aims to turn the tables on McMurtry, who is branding himself as a staunch Trump ally in lockstep with the president ahead of the May 19 primary.

“He’s even worse than a Never Trumper. Todd McMurtry is a Trump hater,” says the ad, which opens with a photograph of Massie and Trump flashing grins and thumbs-ups.

Massie’s commercial then highlights a handful of critical comments McMurtry made about Trump on Facebook, mostly in 2017, the first year of Trump's presidency.

“Sad but true. Trump is the epitome of a weak male,” said one McMurtry post, read in classic attack-ad fashion by the narrator.

“Trump is an idiot,” says another.

“Hillary is right,” McMurtry writes in another comment. “He is temperamentally unqualified to be president.”

Massie’s commercial concludes by tying his primary opponent to Hillary Clinton: “Siding with ‘Crooked Hillary.’ That’s Todd McMurtry, the Trump hater.”

The race in Kentucky’s deeply conservative 4th Congressional District, which spans the northernmost part of the state, underscores how GOP primaries are becoming litmus tests for fealty to Trump. Republican contests in areas from the Philadelphia suburbs to Fort Worth, Texas, are hinging on a simple factor: whether an incumbent House Republican has been sufficiently supportive of the president.

The significance of this test became clear during the 2018 primary season. Former Rep. Mark Sanford (R-S.C.) lost reelection to a challenger who highlighted his denunciations of the president. Two other Trump critics, Sens. Jeff Flake of Arizona and Bob Corker of Tennessee, retired rather than face primary challenges from Trump-aligned opponents when their poll numbers sagged after blowups with Trump.

That has led a small group of Republicans, which now includes Massie, to go to great and unusual lengths to dissuade the president from endorsing a primary opponent. Alabama Rep. Martha Roby withdrew her support for Trump after the release of the lewd “Access Hollywood” tape just prior to the 2016 election, prompting a furious response from local Republicans. So once Trump took office, Roby became a frequent visitor at the White House in hopes of smoothing over her relationship with the president. At the time, Roby was trying to fend off a primary threat from a pro-Trump opponent. She won reelection in 2018 but is retiring in 2020.

Massie’s ad cuts into the main point of his opponent’s campaign. McMurtry, one of the attorneys who represented Covington Catholic student Nicholas Sandmann in his defamation lawsuit against several media outlets, has pointed out that Massie’s voting record is less aligned with Trump less than any other member of the Kentucky congressional delegation, saying that Trump can’t “rely on our congressman’s support.”

Running in a district that Trump won by more than 35 percentage points, McMurtry has vowed there will be no daylight between him and the president. Earlier this month, he tweeted out a picture of the Trump Hotel in Washington.

“Hoping to see my favorite President,” McMurtry wrote.

It’s not the first time a candidate has bought advertising time in South Florida hoping to get the president’s attention. Shortly after launching his Democratic presidential campaign last fall, former New York Mayor Mike Bloomberg ran TV commercials in the area, coinciding with the president’s holiday travel to Mar-a-Lago.

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And Massie’s campaign is making no secret of its intended audience.

“We know the president will be in Florida this weekend, and we want him to know that our primary opponent has not been a supporter of his,” said Massie campaign manager Jonathan Van Norman.

The Massie campaign is spending around $3,000 to air the commercial during Fox News programs this weekend in the West Palm Beach area, including “Fox News Sunday.” The spot is expected to air more than 50 times on Fox News over a 36-hour period.

The campaign will also spend $13,000 to run the ad on Fox News in Kentucky from Feb. 1 through Feb. 10.

The McMurtry campaign responded to the ad by pointing to several pieces of legislation and recent votes on which Massie broke with Trump, including a resolution aimed at curtailing the president’s ability to wage war with Iran.

“Every time President Trump needs him, Massie stabs him in the back,” McMurty campaign manager Jake Monssen said. “It would be great if Thomas Massie’s problem was limited to old Facebook posts. It’s not. His problem is his anti-Trump voting record in the House.”

While Trump has endorsed several House Republicans who are trying to fight off primaries, aides to the president say he is unlikely to intervene in the Kentucky contest — either for or against Massie. While they acknowledge Massie has sometimes opposed the president, they also note that he voted against impeachment in the House.

That has not kept Massie, who is facing the most serious reelection threat of his congressional career, from pursuing a presidential endorsement. Van Norman said the reelection campaign had been seeking Trump’s support.

“Certainly,” Van Norman said, “Congressman Massie would welcome an endorsement from President Trump in his race.”