President Biden’s dedication to protecting the US from partaking in direct fight with Russian forces confronted an sudden check this week, when Poland shocked American officers by providing to show over its assortment of growing older, Russian-made MIG fighters, for final switch to Ukraine.

However the provide got here with a hitch: Poland refused to offer the MIGs on to Ukraine. The deal would solely go ahead if the US, and NATO, did the transferring, after which changed Poland’s fleet with American-made fighter jets. The USA, blindsided by the demand, started to choose aside what was happening. Polish leaders, frightened of incurring Russia’s wrath, and maybe an assault on the air base the place the MIGs launched from, was handing the issue of changing into a “co-combatant” within the conflict off to Washington and its different NATO allies.

The Pentagon all however rejected the thought on Tuesday evening and stated the US had not been consulted. By late Wednesday, Protection Secretary Lloyd J. Austin III had put a stake by the entire concept, telling his Polish counterpart in a cellphone name that the proposed MIG switch was a useless letter, Pentagon officers stated.

“The switch of fight plane might be mistaken for an escalatory step,” John F. Kirby, a Pentagon spokesman, informed reporters.

Within the midst of a remarkably unified alliance, the backwards and forwards was a reminder that the joint effort to punish and finally repel Russia has a 3rd rail that nobody desires to the touch. Ukraine’s allies will present 17,000 anti-tank weapons in six days; they may practice their cyberweapons on Russian targets. However they won’t danger a dogfight over the skies of Ukraine, which, within the minds of many, is certain to convey them totally into the conflict.

That distinction was pushed residence on Wednesday, when Secretary of State Antony J. Blinken, who had initially appeared considerably open to the thought of Poland giving its planes to Ukraine, stated the thought of flying MIG-29 fighter jets to a U.S. air base in Germany for switch to Ukraine lacked a transparent “substantive rationale.”

“The prospect of fighter jets on the disposal of the US Authorities departing from a U.S. NATO base in Germany to fly into airspace contested with Russia over Ukraine raises some critical issues for all the NATO alliance,” Mr. Blinken stated throughout a information convention in Washington.

Then he acquired to his central level: “Our purpose is to finish the conflict, to not broaden it — together with probably broaden it to NATO territory,” Mr. Blinken stated.

Administration officers, when promised anonymity, conceded that the political stress on them to strike a deal to place Ukrainian pilots in cockpits was enormous. Whereas Russia’s air pressure has carried out poorly to this point, Ukraine’s capability to contest the skies with its present fleet is proscribed — and possibly diminishing, as soon as Russia strikes in its subtle air defenses.

So when the US rejected the proposal, Republicans leapt — the primary time there was a partisan breach on technique.

“President Biden ought to clarify precisely why he vetoed fighter jets for Ukraine,” Senator Ben Sasse, Republican of Nebraska and a member of the Senate Intelligence Committee, stated in an announcement.

He argued that the administration was giving Ukraine “Javelins and Stingers from NATO territory,’’ a reference to antitank and antiaircraft weapons. “So why precisely does President Biden suppose that Ukrainian MIGs, flown by Ukrainian pilots, could be shot down over NATO territory whereas they’re on their solution to defend Ukrainian airspace?”

There have been comparable blasts from different Republicans.

In actual fact, the road between sending ammunition and sending weapons is a murky one. And whereas there could also be authorized distinctions, administration officers made clear that they’d little doubt that President Vladimir V. Putin of Russia would regard sending the planes as an escalatory transfer.

The problem began about 10 days in the past when Josep Borrell Fontelles, the European Union’s high overseas coverage and safety official, stated at a information convention that the E.U. nations have been going to supply “combating jets. We’re not speaking about simply ammunition. We’re offering extra essential arms to go to a conflict.”

He later backtracked, saying international locations would individually determine what to do. The concept picked up traction in Congress. Many seemed to Poland, as one in all three nations that would present the MIG fighters — which, by definition, are three many years previous and hardly as much as fashionable requirements. (The Ukrainians need these planes as a result of they know methods to fly them — previous MIGs, left over from Soviet days, make up their air pressure.)

However then Poland started to consider the Russian threats to assault any nation that allowed Ukrainian jets to carry off from their airfields to have interaction Russian forces.

So Poland stated it wished handy the planes over to the U.S. base at Ramstein, Germany, turning it into one thing of a used-plane lot for Chilly Struggle plane. It was as much as the People, they stated, to repair them up and provides them to Ukraine.

Daniel Fried, a former senior State Division official and former U.S. ambassador to Poland, stated the snafu appeared to have began with a miscommunication and snowballed from there.

“It appears like a large number. I believe there’s a chain of miscommunication that resulted in blended alerts to the Poles.”

“Borrell began it,” he stated. “Then the U.S. didn’t be clear with Poles and inadvertently gave blended alerts,’’ a reference to Mr. Blinken’s preliminary, seeming openness to the thought.

Mr. Fried concluded: “The administration wants to not clarify why the MIGs are a nasty concept. They should clarify what they may do to assist the Ukrainians obtain what they wished to realize with the MIGs.”

Michael Crowley contributed reporting from Washington.