West Wing aides have noted that public support goes up for Ukraine funding any time there is a major moment in the conflict. They plan to take advantage of a pair of upcoming international appearances by Ukrainian President Volodymyr Zelenskyy to keep the pressure on Republicans. Zelenskyy is expected to attend next month’s G-20 summit meeting in India before returning to the United States to deliver a speech to the U.N. General Assembly.

The White House will also ramp up public pressure by hammering home the need to defend democracies around the globe as well as the fiscal necessity to thwart Russia — or any future nation with war ambitions — by pointing out the negative economic impact of the war.

“The defense assistance that both parties have come together around has been critical to Ukraine’s ability to beat back Russia’s illegal invasion and to strengthening our alliances in the world,” said White House spokesperson Andrew Bates.

“The president has been very clear that this strategy deters wars of choice and the economic disruption they cause and that we will continue to support Ukraine and our own basic principles as a country,” he said.

But the funding battle is poised to lead to another standoff between the president and Speaker Kevin McCarthy, one that could shape Biden’s legacy and Ukraine’s success in the war.

Biden has placed the defense of Ukraine against Russia’s invasion at the center of his foreign policy, rallying the democracies of the world to help one of their own. The U.S. has spearheaded the effort, corralling NATO and other allies to send billions in military and economic aid. But the jubilation is giving way to fear as Ukraine’s wartime success stalls.

Kyiv’s counteroffensive, purposefully slow to preserve troops and weapons as they wade through minefields and operate without air cover, has helped its forces advance foot-by-foot along the 600-mile front with dug-in Russian forces. But that slow pace has led senior U.S. officials to admit they don’t know how to judge the progress.

The tactics clearly don’t make good politics. Polls suggest Americans are growing weary of supporting Ukraine’s battlefield stalemate, and Republicans are seizing on what they see as an opportunity.

The funding path should be easier in the Senate than the House since Ukraine has been championed by several Republicans, most notably Minority Leader Mitch McConnell. McConnell views support for Ukraine as a piece of his legacy and the West Wing believes he will keep his side largely in line — and, importantly, set a tone for the House talks. But a worsening of the 81-year-old senator’s recent health challenges could upend the calculations.

Still, the Senate will want to put their fingerprints on any spending bill especially after the way the Senate got jammed by the House on the debt ceiling agreement. When the White House sent its funding request last week, the top Republican and Democratic appropriators indicated they would write their own legislation.

For now, McCarthy looms as the White House’s most significant obstacle. He has at times been in the thrall of his party’s far right, which has called for slashing money being sent to the war zone.

Former President Donald Trump, the prohibitive favorite to become the GOP presidential nominee, has questioned the need to back Ukraine and repeated a desire to broker a peace deal with Russia quickly. Officials on both sides of the Atlantic assess that Russian President Vladimir Putin is trying to wait out the upcoming U.S. election, believing that his fortunes in the war could change if a Republican commands from the Oval Office.

Even pro-Ukraine Republicans are hedging against supporting a new deal for Ukraine. Rep. Andy Harris (R-Md.), the House Freedom Caucus’ sole Kyiv-friendly member, said this week that Ukraine can’t win the war and, therefore, the U.S. should reconsider further stocking its defenses.

“It’s not just far-right members,” said a House Republican aide granted anonymity to speak freely. “[Mainstream Republicans are] sympathetic to the cause but we’re throwing money at a conflict that can last for years.”

McCarthy’s office did not return multiple requests for comment.

Financial support for Ukraine, for the most part, still enjoys bipartisan backing. But there is long-running skepticism among House Republicans about continuing to fund the war in Ukraine, and it’s unclear if McCarthy wants to defy them to strike another spending deal with Biden. White House aides and Democratic congressional negotiators expect that the speaker, in order to appease the hard right, will push to make some cuts and could threaten at any point to blow up the package.

Republicans may also ask, according to those close to the process, for some sort of inspector to monitor Ukraine funding to ward off corruption.

But Rep. Don Bacon (R-Neb.), a staunch Ukraine supporter and McCarthy ally, said he would only support a Ukraine package that ensures advanced weapons like the long-range Army Tactical Missile System make it to the battlefield. Without that assurance, he sees no point in further depleting U.S. stocks and spending more money to keep Ukraine at a fighting stalemate with Russia.

“Why keep giving Ukraine weapons that don’t help them win the war?” the House Armed Services Committee member said in an interview. “I don’t want to give more for a gridlock.”

Far-right Republicans are likely to weaponize the domestic-foreign imbalance in the White House’s spending request: $40 billion total, including $24 billion in Ukraine. The emergency supplemental request will bump up against what is expected to be a continuing resolution to keep the government funded for a short, yet-to-be-determined amount of time — another measure unpopular with conservatives.

Senate Majority Leader Chuck Schumer argues that consensus is possible.

“This is not just Democrats. This is not just Joe Biden. The vast majority of the Republican caucus in the Senate and the Republican leader saying we need this supplemental, and we need it for — we need it for Ukraine,” Schumer said. “And I am hopeful that the House will do that.”

Congress has already approved $113 billion in aid for Ukraine including around $70 billion for security assistance; more than 90 percent of it has already been spent or assigned. The new request includes $13.1 billion for military aid to Ukraine and replenishment of Pentagon weapons supplies that have been used for the war effort. An additional $8.5 billion would go for economic, humanitarian and other assistance to Kyiv and other nations affected by the war, while $2.3 billion would be used in an effort to leverage more aid from other donors through the World Bank.

But the chorus of Washington voices who think enough is enough has grown louder.

“The United States’ current level of support for Ukraine is unsustainable militarily, financially and increasingly politically,” said Dan Caldwell, vice president for the Center for Renewing America, who with his colleagues is lobbying House Republicans to oppose the Ukraine spending request.

Proponents argue the need for new funds is urgent. The money Congress initially approved is now down to the single digits at an estimated $6 billion. It’s enough to further provide Ukraine with munitions for Patriot air-defense systems, 155 mm artillery rounds, Javelin anti-tank missiles and spare parts to fix broken-down equipment. U.S. officials say it’s not sufficient, even as the Pentagon finds more dollars in the proverbial couch, to sustain Ukraine for the long haul.

“It’s important that we put the national interest here first and that [McCarthy] not continue to be led around by the nose by his farthest right and most extreme members,” said Sen. Chris Van Hollen (D-Md.). “I am confident that at the end of the day we’ll get something through. I think there’s going to be a lot of — I think there’ll be some bumps along the way.”