Senate Republicans who voted to advance aid for Ukraine last week are taking heavy incoming from allies of former President Trump, who are calling them out publicly and threatening primary challenges after they defied Trump’s calls to oppose the package.

Donald Trump Jr., the ex-president’s eldest son, has led the charge against the 22 Republicans who backed the national security supplemental, many of whom are allies of Senate Minority Leader Mitch McConnell (R-Ky.).

He called for Sen. Joni Ernst (R-Iowa) to get a primary challenge, and for West Virginia primary voters to reject the gubernatorial bid of Moore Capito, the son of Sen. Shelley Moore Capito (R-W.Va.).

In another instance, Texas Attorney General Ken Paxton (R) a major backer of Trump, took aim at Sen. John Cornyn (R-Texas), one of McConnell’s top allies, writing on social media, “Unbelievable that [Cornyn] would stay up all night to defend other countries borders, but not America.”

While some believe the Capito gubernatorial threat, in particular, was a low blow, the frustration from Trump’s orbit is palpable and is laying bare the fissures between it and GOP leadership.

“The last month exposed the problems that come with a GOP leadership team that has no relationships with the likely Republican nominee for president,” one Senate GOP aide said. “It further exposes the disconnect between Republican lawmakers largely in D.C. compared to where our voters are.”

The security bill includes $60 billion in military and economic assistance for Ukraine and $14 billion for Israel, along with monies for the Indo-Pacific region and humanitarian purposes.

On top of the Ernst and Capito remarks, Trump Jr. also took aim at Cornyn and Senate Minority Whip John Thune (R-S.D.) — two of the leading contenders to eventually replace McConnell — over their Ukraine aid votes.

But whether the barbs will have much impact is an open question, strategists and aides across the GOP spectrum say.

They are quick to note that being, or not being, in the good graces of the former president is always a fluid situation that can be changed in short order, for better or for worse.

“Trumpworld has a short memory if you get on board,” the Senate GOP aide said.

They also note the insular nature of the Senate, with leadership elections and votes for various bills, including Ukraine aid, rarely determined from outside of the chamber.

“The Senate is notoriously immune from pressure from the outside, and the harder they push the less likely they are to get what they want. The United States Senate is very similar to former President Trump in that way,” one GOP operative told The Hill. “The outside game never works with the Senate.”

Despite Trump’s power and heft with the GOP base, even his voice has limitations sometimes.

For example, Trump and his allies came up empty in the 2022 cycle to recruit a challenger to Thune after he said the 2020 electoral count would go down like a “shot dog.”

The No. 2 Senate Republican ultimately won reelection by 43 points — a larger margin of victory than South Dakota Gov. Kristi Noem (R), a top Trump ally, raked in that year.

Nevertheless, Republicans are taking notice of the threats, with Ernst atop that list.

Trump Jr. also floated Matthew Whitaker, a top Trump backer who served as acting attorney general briefly before William Barr took over the post, to challenge her.

While the Republicans note that one vote — especially aid to Ukraine — likely wouldn’t be enough to bring a member down, it could be a piece to a puzzle.

“One individual vote rarely ends a Senate career, but … what happens when it’s connected to a broader theme is the problem,” a second GOP operative said. “For [Ernst], if you’re within the [Trump] inner circle right now, this is the lady who was with Nikki Haley the night before the [Iowa caucuses], and then she’s doing this; and is she supportive of him? That’s the bigger picture within Trumpworld.”

Despite her appearance with Haley, Ernst remained officially neutral through the caucuses and has declined to weigh in with a primary endorsement since.

Half of Senate GOP leadership has endorsed Trump thus far, including Sen. John Barrasso (R-Wyo.), who backed him ahead of Iowa, and Sen. Steve Daines (R-Mont.), who did so early last year. Sen. Capito endorsed the ex-president in late January.

As for Trump, he has not added his two cents to his eldest son’s remarks. His social media posts reiterated calls for lawmakers to oppose the security spending package and have taken aim at NATO countries he says have not lived up to their obligations. Some of his supporters have also followed his lead and called for the funds to be given as a loan rather than a grant.

The battle over Ukraine funding ratcheted up again Friday after Alexei Navalny, the Russian opposition leader and President Vladimir Putin’s preeminent foe, died in a Russian penal colony, raising more questions about the future of that possible aid to Kyiv.

Speaker Mike Johnson (R-La.) said is not expected to bring the Senate bill as is up in the House, with a group of bipartisan lawmakers crafting a smaller, more targeted bill instead for possible consideration.

But in a statement reacting to Navalny’s death, he said that while Congress “debates the best path forward to support Ukraine,” the U.S. and its partners “must be using every means available to cut off Putin’s ability to fund his unprovoked war in Ukraine.”