After initially supporting the Biden administration's efforts to punish Russia for invading Ukraine, Republican senators have shifted away from the White House amid a difference on bolstering Ukraine's defenses.

Sen. Lindsey Graham, R-S.C., lambasted President Joe Biden for “folding like a cheap suit” after deciding against the transfer of Soviet-era fighter jets from Poland to Ukraine. Graham, who has walked back calls for Russians to assassinate President Vladimir Putin, accused Biden of being intimidated by Moscow’s threats.

“What I think happened is that the Russians told Biden and his team that if you send these MiGs, that will be an escalation and they were intimidated by Putin," Graham said on Fox News.

On Thursday, more than 40 Republican senators wrote an open letter to Biden in which they strongly disagreed with the decision to not transfer aircraft and air defense systems to Ukraine from Poland.

After initially endorsing the deal, officials reversed course after the Pentagon and the U.S. intelligence community warned of serious consequences. Calling it "high risk," the administration cautioned such a move could result in greater escalation after Putin suggested that it would be interpreted as entering the conflict as a belligerent.

This answer did not satisfy Republican senators who sit on the Senate Intelligence Committee. In an exchange on Wednesday with Director of National Intelligence Avril Haines, ranking member Sen. Richard Burr of North Carolina questioned whether this justification was more a cover for policy decisions than based on intelligence.

Sen. Tom Cotton, R-Ark., similarly accused the Biden administration of looking to the intelligence community "to provide cover" for its own reluctance to make a decision. Pointing to the provision of U.S. anti-aircraft and anti-tank missiles to Ukrainian forces, Cotton said that he did not understand how jets were any more escalatory than these systems.

“I gotta say, I don’t think there’s a lot of common sense in this distinction," Cotton remarked to Director of the Defense Intelligence Agency Lt. Gen. Scott Berrier.

The backlash to Biden holding back on transferring the MiGs from a U.S. military base in Germany to Poland has also drawn scrutiny from some Democrats. In a Senate hearing on Thursday, Sen. Jeanne Shaheen of New Hampshire called the reversal a sign of “indecision” and “bickering" on the part of the administration.

The Biden administration's approach has been for stronger economic punishment against Russia than many had expected. Together with the European Union, Japan and others, the sanctions have slashed the value of the Russian ruble and shuttered Moscow’s stock exchange for days. At the same time, the U.S. targeted the assets of Kremlin-backed oligarchs worldwide and banned all imports of Russian oil.

But Biden has repeatedly refused to take harder measures in support of Ukraine. Since December, he ruled out deploying U.S. troops to Ukraine in the event of a Russian invasion and more recently has rebuked requests from Ukraine’s embattled President Voldomyr Zelensky to establish a no-fly zone out of a risk of entering a nuclear war with Russia.

The split with Republicans comes after weeks of unity from their caucus in opposing Russia’s war in Ukraine. Last December, Senate Majority Leader Mitch McConnell, R-Ky., said he backed Biden’s choice to pursue diplomacy to avert a war. Other Republicans, like Sen. Marco Rubio of Florida, have agreed that implementing a no-fly zone would be risky.

Support from these corners has waned after Biden decided against the jet transfer from Poland to Ukraine.

"It is American hesitancy and weakness which our adversaries see as an invitation,” McConnell said in remarks on the Senate floor. "American strength is not the provocation. American weakness is."