WASHINGTON (AP) — Top Biden administration officials were laboring on Wednesday to try to reach a last-minute deal for wartime aid for Ukraine by agreeing to Senate Republican demands to bolster U.S.-Mexico border policies to cut crossings.

Homeland Security Secretary Alejandro Mayorkas was expected to resume talks with Senate negotiators even as advocates for immigrants and members of President Joe Biden's own Democratic Party fretted about the policies under discussion. Some were planning to protest at the Capitol, warning of a return to Trump-like restrictions.

Congress is scheduled to leave Washington on Thursday, leaving little time to reach an agreement on Biden's $110 billion request for Ukraine, Israel and other national security needs. But White House officials and key Senate negotiators appeared to be narrowing on a list of priorities to tighten the U.S.-Mexico border and remove some recent migrant arrivals already in the U.S., raising hopes that a framework could be within reach.

"This is difficult, very difficult," Senate Majority Leader Chuck Schumer, D-N.Y., said in a speech on the Senate floor on Wednesday. "But we're sent here to do difficult things."

Among the proposals being seriously discussed, according to several people familiar with the private talks, are plans to allow Homeland Security officials to stop migrants from applying for asylum at the U.S. southern border if the number of total crossings exceeds daily capacity of roughly 5,000. Some one-day totals this year have exceeded 10,000.

Also under discussion are proposals to detain people claiming asylum at the border, including families with children, potentially with electronic monitoring systems.

Negotiators are also eyeing ways to allow authorities to quickly remove migrants who have been in the United States for less than two years, even if they are far from the border. But those removals would only extend to people who either have not claimed asylum or were not approved to enter the asylum system, according to one of the people briefed on the negotiations.

The policies resemble ones that President Donald Trump's Republican administration tried to implement to cut border crossings, but many of them were successfully challenged in court. If Congress were to make them law, it would give immigration advocates very little legal ground to challenge the restrictions for those seeking asylum.

Advocates for immigrants, who are planning demonstrations across the Capitol on Wednesday, warned of a return to anti-immigrant policies and questioned whether they would even address problems at the border.

"I never would have imagined that in a moment where we have a Democratic Senate and a Democratic White House we are coming to the table and proposing some of the most draconian immigration policies that there have ever been," said Maribel Hernández Rivera, American Civil Liberties Union director of policy and government affairs.

The Senate negotiations had also found some agreement on raising the threshold for people to claim asylum in initial credible fear screenings.

Even if a deal can be struck and passed in the Senate, House Speaker Mike Johnson of Louisiana, a Republican, would also need to push the legislation through his chamber, where there will likely be opposition from both parties. Hard-line conservatives complain the Senate proposals do not go far enough, while progressive Democrats and Hispanic lawmakers are opposed to cutting off access to asylum.

Earlier in the week, many members in the Capitol predicted that a deal before Congress left for a holiday break was unlikely. Pessimism was running high even after Ukrainian President Volodymyr Zelenskyy visited on Tuesday and implored lawmakers to renew their support for his country's defense against Russia's invasion.

But after Mayorkas met with key Senate negotiators for nearly two hours on Tuesday, lawmakers emerged with a new sense of optimism.

Sen. Chris Murphy of Connecticut, who is leading the talks for Democrats, said the meeting included "a group that can land this deal if everybody's ready to close."

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Associated Press writers Elliot Spagat, Seung Min Kim and Rebecca Santana contributed to this report.