WASHINGTON (AP) — Ukrainian President Volodymyr Zelenskyy's visit to Washington this week comes at a critical juncture for his alliance with the United States as Republican leaders in Congress diverge on how to send more military and humanitarian aid to the country.

President Joe Biden is seeking an additional $24 billion in security and humanitarian aid for Ukraine, in line with his promise to help the country for “as long as it takes” to oust Russia from its borders.

But ratification of Biden's request is deeply uncertain thanks to a growing partisan divide in Congress about how to proceed.

Republican House Speaker Kevin McCarthy has told reporters that he wants more Ukraine aid to be debated on its own merits as a standalone bill, rather than attaching it to other priorities like government funding.

But the Senate has other ideas. Leaders in the chamber would like to combine the Ukraine aid with other priorities, such as a short-term spending bill that will likely be needed to avoid a shutdown at the end of September.

The differing approaches threaten to become a stalemate that could easily delay future rounds of American assistance to Ukraine, raising the stakes for Zelenskyy as he makes his first visit to the United States since his surprise address to Congress at the end of 2022. In that speech, Zelenskky thanked “every American” for support as then-House Speaker Nancy Pelosi, D-Calif., and Vice President Kamala Harris dramatically unfurled a Ukrainian flag behind him.

Nine months later, with Republicans now in control of the House majority, there is growing wariness among voters about continued support for Ukraine as Russia turns its invasion into a costly war of attrition. In Congress that skepticism is concentrated among House Republicans, where many share former President Donald Trump's “America First" approach and want to halt the aid entirely.

The U.S. has approved four rounds of aid to Ukraine in response to Russia’s invasion so far, totaling about $113 billion, with some of that money going toward replenishing U.S. military equipment sent to the frontlines. Most members of the House and Senate support the aid, viewing defense of Ukraine and its democracy as a global imperative.

McCarthy has stressed the need for oversight of Ukrainian assistance but has also been critical of Russia, criticizing the country's “killing of children” in a speech this summer. But he is juggling a desire to help Ukraine with the political realities at home, which include a demand from many in his party to slash government spending.

In some ways, attaching Ukraine aid to other pressing matters could improve the odds of passing it quickly. Some lawmakers will be more inclined to vote for Ukraine assistance if it gets included with say, disaster relief for their home state.

But the maneuver would also deeply divide House Republicans and is sure to inflame critics of McCarthy who are threatening to oust him from the speakership.

“I don’t know why they would want to put that onto a CR," McCarthy said, using Washington parlance for a short-term continuing resolution that keeps agencies funded. “I think it should be discussed on its own.”

Meanwhile, Senate Republican leader Mitch McConnell has put Ukraine aid at the top of his to-do list, and has been speaking from the Senate floor for weeks about the urgency he sees to act.

He brought in inspectors general last week to brief GOP senators on how U.S. aid is being tracked to address concerns about waste and fraud. And in one of his speeches on the Senate floor, McConnell responded to critics who say that the U.S. has borne too much of the burden on Ukraine by pointing to the assistance also flowing from European nations.

“In fact, when it comes to security assistance to Ukraine as a share of GDP, 14 of our European allies are actually giving more,” McConnell said.

Senate Majority Leader Chuck Schumer, D-N.Y., and McConnell have called for senators to meet with Zelenskyy on Thursday morning.

Sen. Thom Tillis, R-N.C., said he believes aid should be provided as soon as possible, and the legislative vehicle for that is unlikely to be a stand-alone bill.

“I for one think we ought to go ahead and get it done,” Tillis said. “We have to get the Ukraine funding done in a time that doesn't produce a lapse, at least a perceived lapse, because I think that's a strategic win for Putin and I don't ever want Putin to have a strategic win.”

But Rep. Ken Calvert, R-Calif., warned against adding Ukraine aid to the short-term spending bill. He said the focus needs to be on first passing an overall defense spending bill as well as the other spending bills.

“We can't divert attention outside of that,” Calvert said. “There's significant munitions within Ukraine right now I think to get through the end of the year."

Rep. Mike Garcia, R-Calif., said he's not necessarily opposed to more Ukrainian assistance, but he said the average American doesn't know how the war is going, and the average member of Congress can't say, either.

“Tell us what you're doing with the money, and let's have a debate on the floor about this funding and not ramming it down our throats,” Garcia said.

House Republicans hope to bring up for a vote this week a stopgap spending bill that doesn't include Biden's aid package for Ukraine.

“I cannot think of a worse welcome for President Zelenskyy who visits us this week than this House proposal, which ignores Ukraine entirely,” Schumer said.

Still, Rep. Michael McCaul, the top Republican on the House Committee on Foreign Affairs, voiced confidence that Ukraine aid will continue.

“It has to pass. What I hear from our NATO allies ... is that if the United States is not in, the whole thing falls apart,” McCaul said.