WASHINGTON (AP) — Politically freighted border security negotiations are teetering just days before a potential new government shutdown. The turmoil is testing the changed balance of power in Washington, with lawmakers engaged in a sparring match over immigration policy that is challenging their ability to reach any accord.

Republicans say Democratic demands to limit immigrant detentions by federal authorities are a deal breaker — eclipsing the border wall issue for now — and represent overreach by top Democrats like House Speaker Nancy Pelosi of California.

The two sides also remained separated over how much to spend on President Donald Trump’s promised border wall. A Friday midnight deadline is looming to prevent a second partial government shutdown.

Lawmakers hoped to get the talks back on track at a meeting on Monday afternoon.

Rep. Kay Granger of Texas, one of the Republican negotiators, gave an upbeat assessment. She said the talks are in “better shape today” and expressed optimism about reaching a deal before the deadline.

The plan is to keep pushing for a deal, in part because the underlying spending measure funds a bevy of Cabinet departments and represents months of work on Capitol Hill. A collapse of the negotiations could imperil budget talks going forward that are required to prevent steep spending cuts to the Pentagon and domestic agencies.

But the negotiations hit a rough patch Sunday amid a dispute over curbing Immigration and Customs Enforcement, or ICE, the federal agency that Republicans see as an emblem of tough immigration policies and Democrats accuse of often going too far.

Trump blamed Democrats in the migrant detention dispute, tweeting, “The Democrats do not want us to detain, or send back, criminal aliens! This is a brand new demand. Crazy!”

Trump met Monday afternoon with top advisers in the Oval Office to discuss the negotiations before heading to Texas for a rally. Asked by reporters if there was going to be another shutdown, Trump replied: “That’s up to the Democrats.”

The fight over ICE detentions goes to the core of each party’s view on immigration. Republicans favor rigid enforcement of immigration laws and have little interest in easing them if Democrats refuse to fund the Mexican border wall. Democrats despise the proposed wall and, in return for border security funds, want to curb what they see as unnecessarily harsh enforcement by ICE.

People involved in the talks say Democrats have proposed limiting the number of immigrants here illegally who are caught inside the U.S. — not at the border — that the agency can detain.