WASHINGTON (AP) — House Speaker Mike Johnson took a strong stand Friday against a bipartisan Senate deal to pair border enforcement measures with Ukraine aid, sending a letter to colleagues that aligns him with hardline conservatives determined to sink the compromise on border and immigration policy.

Johnson, a Louisiana Republican, said that the legislation would have been "dead on arrival in the House" if leaked reports about the legislation were true. While a core group of senators negotiating the deal have not yet released text of the bill, it has already come under fire from Republicans, including Donald Trump, the likely presidential nominee, who eviscerated the deal this week as a political "gift" to Democrats.

Johnson in the letter said, "Rather than accept accountability, President Biden is now trying to blame Congress for what HE himself intentionally created."

The message added to the headwinds facing the border and Ukraine deal, closing a week in which Senate Republican Leader Mitch McConnell acknowledged to his colleagues that the legislation faced tough opposition from Trump that could force them to pursue Ukraine aid another way. He later clarified that he was still supportive of pairing border measures with Ukraine aid — an arrangement that Senate Republicans initially demanded to gain their votes for funding Ukraine's war.

The diminishing prospects for a deal leave congressional leaders with no clear path to approving a $110 billion White House request for emergency funding for Ukraine, Israel, immigration enforcement and other national security needs. President Joe Biden has made it a top priority to bolster Kyiv's defense against Russia, but his administration has run out of money to send ammunition and missiles. Ukraine supporters warn that the impasse in Congress is already being felt on battlefields and leaving Ukrainian soldiers outgunned.

Johnson was already deeply skeptical of any bipartisan compromise on border policy, which would be necessary to clear the Senate. On Friday, he again pointed to a sweeping set of immigration measures that the House passed last year as being the answer to the nation's border challenges. But that bill failed to gain a single Democratic vote then and has virtually no chance of picking up Democratic support now.

As they enter an election year, Republicans are seeking to drive home the fact that historic numbers of migrants have come to the U.S. during Biden's presidency. His administration has countered that global unrest is driving the migration and has sought to implement humane policies on border enforcement.

Leaning into the push on immigration, the speaker said in his letter that the House would hold a vote on impeaching Homeland Security Secretary Alejandro Mayorkas "as soon as possible" after a committee advances articles of impeachment against him next week. Johnson also said he was standing with Texas Gov. Greg Abbott, who has refused to give federal Border Patrol agents access to a riverfront park that is a popular corridor for migrants illegally entering the U.S.

But the speaker is also under potential pressure himself.

If the Senate were to pass an immigration and Ukraine package, he would face a decision about whether to bring the measure to the floor. And while the speaker is skeptical of continued funding for Ukraine, he has also expressed support for halting Russian President Vladimir Putin's advance in Europe.

At the same time, hardline House conservatives have become vocal opponents of any compromise on immigration policy. Rep. Marjorie Taylor Greene, a hard-right Republican of Georgia, has threatened to initiate an effort to oust Johnson if he put the Senate deal on the House floor.

"This bill represents Senate Republican leadership waging war on House Republican leadership," said Sen. Ted Cruz, a Republican of Texas, at a news conference this week.

Still, other Republicans have lamented that conservatives are throwing away an opportunity to gain a victory on an issue they have talked about far more than Democrats. The proposal would enact tougher standards on migrants seeking asylum as well as deny asylum applications at the border if daily migrant encounters grew to be unmanageable for authorities.

But reports about the details of the bill among conservative advocacy groups and in conservative media have focused on the measures intended to aid migrants already in the country.

Opposition from the right has stymied efforts to reform immigration law in Congress for decades. Trump allies have argued that Congress does not need to act because presidents already have enough authority to implement tough border measures.

Johnson echoed that sentiment in his letter, arguing that Biden could start to fix the border problems "with the stroke of a pen."

Sen. Markwayne Mullin, an Oklahoma Republican, said earlier this month that conservative reports on the bill had "ginned up a lot of the base" voters against the proposals, even as the policy represented meaningful changes to immigration enforcement.

"This is a national security issue," Mullin said. "And if you're waiting until another president gets in, you're playing politics with it."