WASHINGTON — President Volodymyr Zelensky’s triumphant visit to Washington ended with promises of billions more in U.S. support for Ukraine, but not what he wanted most: American battle tanks, fighter jets and long-range precision missiles.
The United States has repeatedly said there are weapons it will not send to Ukraine to battle Russia’s invading forces. But as the last 10 months of war have shown, the limits of U.S. support have shifted in Ukraine’s favor, and Mr. Zelensky may yet get what he wants.
After his daring 10-hour dash to the nation’s capital on Wednesday, Mr. Zelensky left with nearly $2 billion in new arms and equipment — as well as a likely commitment from Congress for nearly $50 billion in additional aid next year.
And while Mr. Zelensky did not get everything on his wish list, John Kirby, a National Security Council spokesman, said on Thursday that the United States was committed to providing the equipment that Ukraine needs, although he declined to provide specifics.
“Any president, any commander in chief, in similar circumstances would want as much as you can get as fast as he can get it, and we’re committed to doing our part and helping in that regard,” Mr. Kirby said.
He added, though, that Mr. Biden and Mr. Zelensky did not spend a majority of their meeting going over each of Ukraine’s requests. The discussion was not “driven by a list of additional capabilities. There was a much broader, deeper discussion about the situation in Ukraine and what the future portends,” he said.
“Rest assured there will be additional capabilities going into Ukraine,” Mr. Kirby said. “Now, what they are and how much of what they are, that has yet to be determined.”
Mr. Zelensky’s trip was a vivid demonstration of his strategy for wooing and pressuring allies. He mixed appreciation for the aid provided by the United States with growing demands for weaponry, knowing that he will not get all of what he wants but believing the combination of his continued requests and shifts on the battlefield will lead Washington to recalibrate its own assessments of what additional systems Ukraine can receive without risking a dangerous escalation with Russia.
Ukrainian officials have broadcast their top battlefield requests for months, most recently in a tweet labeled “My Christmas Wishlist” from Mykhailo Podolyak, an adviser to Mr. Zelensky.
Mr. Biden approved one item on that list, a battery of Patriot air defenses, on Wednesday. But the administration has declined to offer or help provide the four others, including battle tanks and long-range missiles.
In a news conference on Thursday, President Vladimir V. Putin played down the importance of the Patriot, saying Russia would find a way to defeat it.
“An antidote will always be found,” he said at the Kremlin. “This is simply prolonging the conflict — that’s it.”
In some respects, the Biden administration’s acceptance of risk has increased as the war has gone on. Some weapons systems that were off the table early in the war, like the HIMARS rocket artillery and the Patriot missile defense system, have since been approved and either are in the fight or on the way.
But some American officials argue that it is the nature of the war that has changed, not the level of risk the White House will tolerate. Ukraine had a greater need for the HIMARS system once the war became a battle of artillery and Russian command posts pulled back off the front lines. The Biden administration decided to send the Patriot battery when Russia began launching sustained attacks on Ukraine’s electrical infrastructure as winter set in.
Both the HIMARS and Patriot systems require trained teams to operate them, so there is a cost to Ukraine to pull experienced soldiers off the front lines to learn how to use them. And the United States has only wanted to do that once they were sure the more sophisticated systems could make a real difference.
The administration’s current no-go weapons fall into three basic categories with some overlap, administration officials say.
The first group includes weapons like the long-range missiles called ATACMS, with a range of some 190 miles. The administration fears that if Ukraine gets in a bad enough bind, it could use the missiles to strike targets in Russia, prompting Mr. Putin to widen the war.
When asked about the missiles at a joint news conference with Mr. Zelensky on Wednesday, Mr. Biden cautioned that sending the arms could rupture NATO unity in support of Ukraine. “They’re not looking to go to war with Russia,” he said of the alliance. “They’re not looking for a third world war.”
Some former American commanders reject the administration’s reasons for holding back pivotal weapons at this crucial time in the war.
“The administration continues to overestimate the risk of escalation and underestimate Ukraine’s cleverness and innovative ways of fighting,” said Frederick B. Hodges, a retired lieutenant general and a former top U.S. Army commander in Europe.
A second category covers weapons like armed MQ-1C Gray Eagle and MQ-9 Reaper drones, which proponents said would enable Ukraine to attack a broader array of targets or spot them for other Ukrainian strikes. But Pentagon officials have expressed concerns that if those drones are shot down or crash, Russia could recover them and exploit their advanced technology.
A third category covers weapons like the Abrams battle tank and F-16 fighter jets, some of the most advanced weapons in America’s arsenal. Pentagon officials say Ukraine already has enough tanks and fighter jets from other countries. More important, the officials say, the systems take months to learn how to use and require complex maintenance, usually done by civilian contractors, who might be unable to work safely in Ukraine.
“These are tough choices,” said Representative Jason Crow, a Colorado Democrat who serves on both the House intelligence and armed services committees. He said he supports sending Ukraine the ATACMS and F-16s, but not the battle tanks.
Senator Christopher S. Murphy, Democrat of Connecticut and a member of the Foreign Relations Committee, said Ukraine needs additional munitions that the United States cannot easily provide.
“We simply don’t have the stocks to supply, nor do we make the munitions that much of their equipment fires,” Mr. Murphy said.
“What Ukraine needs is enough firepower to show Putin the limits of his power,” Mr. Murphy said. “Putin is never going to meaningfully come to the table unless he has seen in real terms where his power stops. And so that means you have to be perhaps willing to fund a stalemate for a period of time.”
Mr. Murphy also acknowledged the prospect that with a divided Congress — Republicans take control of the House next month, while Democrats will retain their majority in the Senate — aiding Ukraine may soon prove even more difficult.
“Zelensky is always asking for the sky and that’s perfectly appropriate, and it’s our job to make sure his job is nimble enough to meet the moment,” Mr. Murphy said. “We also do have an obligation to the taxpayers to not waste money.”
With each new request from Ukraine for another advanced capability, the United States has tried to assess how Mr. Putin might react by looking at the Kremlin’s comments and at how Russia has responded in the past when the United States has aided its allies and partners in Europe.
One thing above all others has influenced the debate within the administration over what weapons system to give Ukraine: Russia’s restraint in keeping the war contained.
Russia has steadily increased the brutality and breadth of its attacks against Ukraine, killing civilians on the march to Kyiv, the capital, deporting children from occupied areas and now trying to break the will of the Ukrainians by attacking the electrical infrastructure to plunge the country into cold and darkness.
But Moscow so far has not let its war spill over into NATO territory. American officials continue to insist they have seen nothing that indicates Russia has decided to expand its attacks beyond Ukraine.
There have been no stepped-up cyberattacks by Russian intelligence agencies on NATO allies, and no evidence that Russia has conducted any sabotage attacks on allied countries.
Mr. Putin’s unwillingness to fight NATO directly has been key to the alliance’s ability to supply Ukraine with a steady flow of arms and ammunition, the very supplies that have kept Kyiv in the fight. Mr. Putin has shown he will accept high levels of international support for Ukraine, as long as those weapons are used in Ukraine. That, U.S. officials said, is the critical calculus: whether Mr. Putin will see a weapons system as something meant to attack Moscow, or something meant to be used inside Ukraine.
It is important, these U.S. officials say, not to give Mr. Putin an excuse to expand the war.
Edward Wong contributed reporting.