US Rep. Thomas Massie (R-KY) leaves a meeting of the House Republican Conference in the US Capitol on Wednesday, June 4, 2025. Photo: Tom Williams/CQ Roll Call/Sipa USA via Reuters Connect

The heated Republican primary battle in Kentucky between incumbent Rep. Thomas Massie and Trump-backed challenger Ed Gallrein is set to come to a close on Tuesday in what has become one of the most closely watched congressional fights in the US, one which could have seismic ramifications for the future of the Republican Party’s relationship with Israel.

The race, now considered the most expensive House primary in US history, has evolved far beyond a local Kentucky contest. Instead, it has become a national referendum on the direction of the Republican Party under US President Donald Trump, the limits of ideological dissent within the GOP, and the growing divide between traditional pro-Israel conservatives and a rising faction of right-wing isolationists skeptical of American support for the Jewish state, Washington’s closest ally in the Middle East.

Though Massie was expected to cruise to reelection in the ruby-red Kentucky district, his quest to secure his seat has been made far more daunting after Trump made defeating Massie a personal political mission. Trump, accusing Massie of siding with Democrats to block his agenda and demoralizing the Republican base, has endorsed Gallrein, a retired Navy SEAL officer and spent months pummeling the incumbent with a barrage of public insults.

In a May 18 social media post, Trump lambasted Massie as “the worst congressman in the history of our country.”

“I’m in the Oval Office, and we’re in a fight with the worst congressman in the history of our country,” Trump said on Truth Social. “His name is Thomas Massie, he’s from Kentucky and I hope you’re going to put him out of business tomorrow, he is so bad.”

The Kentucky congressman, a libertarian-leaning conservative long known for opposing federal spending and challenging Republican leadership, broke sharply with Trump over several major issues in recent months, including Iran policy, foreign aid, and the administration’s posture toward Israel during escalating regional tensions in the Middle East.

Though Massie maintains an extensive history of voting down foreign aid to virtually every country, not just Israel, his sharp criticisms toward the Jewish state and its supporters have drawn the ire of many GOP voters. Massie has accused the America Israel Public Affairs Committee (AIPAC), the premier pro-Israel lobbying group in the US, of deploying “babysitters” to monitor and police the votes of lawmakers and prevent dissent around issues regarding Israel and the Middle East. He has also accused Israel of targeting civilian infrastructure in its military campaigns, omitting that terrorist groups such as Hamas and Hezbollah repurpose these locations to store munitions or launch missiles.

Recently, Massie drew backlash from Jewish groups after he posed for a photo with an individual wearing a shirt emblazoned with the phrase “American Reich,” a direct reference to the Nazi regime. Massie has not commented on the incident or distanced himself from the individual.

Massie has also come under fire over an advertisement released by a pro-Massie super PAC targeting billionaire Republican donor Paul Singer, a prominent Jewish supporter of pro-Israel causes who has backed efforts to defeat the incumbent.

The ad characterizes Singer as a “pro-trans billionaire” and features a rainbow-colored Star of David behind his image while attacking Gallrein’s allies.

Massie’s criticism of US support for Israel and his resistance to interventionist foreign policy drew fierce backlash from pro-Israel organizations and Republican donors, many of whom quickly consolidated behind Gallrein, a relatively unknown Kentucky Republican who has embraced Trump’s America First movement while simultaneously affirming strong support for Israel and the US-Israel alliance. The attempt to unseat Massie has attracted roughly $19 million in outside spending, with pro-Israel advocacy groups, MAGA-aligned organizations, and conservative super PACs flooding Kentucky airwaves with ads portraying the Kentucky firebrand as increasingly out of step with Republican voters.

For many pro-Israel Republicans, the race represents an early test of whether the GOP will tolerate lawmakers who oppose robust American backing for Israel during a period of heightened regional instability. The race also comes at a time in which antisemitism and anti-Israel sentiment have become points of contention within the GOP. Though older Republican voters continue to support Israel in substantial numbers, a growing number of polls indicate that younger Republican voters are far more skeptical of the US-Israel alliance, with many wanting to end aid to Israel and cease foreign military campaigns.

Massie has argued that his foreign policy views reflect constitutional conservatism and opposition to “forever wars.” But critics inside the Republican Party say his approach increasingly mirrors the isolationist wing of the American right that seeks to reduce US commitments abroad, including support for Israel.

Gallrein, by contrast, has framed the election as a battle for peace through strength, aligning himself closely with Trump’s aggressive posture toward Iran and emphasizing unwavering support for Israel’s security.

The primary also carries broader implications for Trump’s continued dominance over the Republican Party. Unlike many previous Trump critics who came from the GOP’s moderate wing, Massie is a staunch conservative with strong grassroots credibility among libertarians and Tea Party voters.

Though the race is expected to be very close, Gallrein has amassed substantial momentum in the closing stretch of the competition. A recent poll showed Gallrein leading Massie 53 percent to 45 percent among likely GOP voters in the state’s 4th Congressional District.

A Massie defeat would likely send a powerful message to Republicans nationwide that opposition to Trump — particularly on foreign policy and Israel — carries enormous political risk, even for deeply conservative incumbents.

A victory for Massie, however, could embolden a small but growing bloc of right-wing lawmakers skeptical of foreign intervention and willing to publicly challenge both Trump and the GOP’s traditionally hawkish pro-Israel establishment.

With polling tightening in recent days and turnout expected to be high, political observers across Washington, Jerusalem, and conservative media circles are watching Kentucky closely.