WASHINGTON — Congress lopsidedly approved a border security compromise Thursday that would avert a second painful government shutdown, but a new confrontation was ignited — this time over President Donald Trump’s plan to bypass lawmakers and declare a national emergency to siphon billions from other federal coffers for his wall on the Mexican boundary.

Money in the bill for border barriers, about $1.4 billion, is far below the $5.7 billion Trump insisted he needed to build a wall along the Mexican boundary and would finance just a quarter of the 200-plus miles he wanted. The White House said he’d sign the legislation but act on his own to get the rest, a move that prompted immediate condemnation from Democrats and threats of lawsuits from states and others who might lose federal money or said Trump was abusing his authority.

The uproar over what Trump would do next cast an uncertain shadow over what had been a rare display of bipartisanship in Congress to address the grinding battle between the White House and lawmakers over border security.

The Senate passed the legislation 83-16, with both parties solidly on board. The House followed with a 300-128 tally, with Trump’s signature planned Friday.

Both margins were above the two-thirds majorities needed to override presidential vetoes, though one wasn’t expected and lawmakers sometimes back a president of the same party in such battles.

Lawmakers exuded relief that the agreement had averted a fresh closure of federal agencies just three weeks after a record-setting 35-day partial shutdown that drew an unambiguous thumbs-down from the public. But in announcing that Trump would sign the accord, White House Press Secretary Sarah Sanders also said he’d take “other executive action, including a national emergency.”

In an unusual joint statement, House Speaker Nancy Pelosi, D-Calif., and Senate Minority Leader Chuck Schumer, D-N.Y., said such a declaration would be “a lawless act, a gross abuse of the power of the presidency and a desperate attempt to distract” from Trump’s failure to force Mexico to pay for the wall, as he’s promised for years.

Pelosi and Schumer also said “Congress will defend our constitutional authorities.” They declined to say whether that meant lawsuits or votes on resolutions to prevent Trump from unilaterally shifting money to wall-building, with aides saying they would wait to see what he does.

Democratic state attorneys general said they would consider legal action to block Trump. Puerto Rico Gov. Ricardo Rossello told the president on Twitter “we’ll see you in court” if he makes the declaration.

Despite widespread opposition in Congress to proclaiming an emergency, including by some Republicans, Trump is under pressure to act unilaterally to soothe his conservative base and avoid looking like he’s surrendered in his wall battle.

The abrupt announcement of Trump’s plans came late in an afternoon of rumblings that the president — who’d strongly hinted he’d sign the agreement but never definitively — was shifting toward rejecting it. That would have infused fresh chaos into a fight both parties are desperate to leave behind.

“Let’s all pray that the president will have wisdom to sign the bill so the government doesn’t shut down,” Sen. Charles Grassley, R-Iowa, said Thursday.