Donald Trump’s emergency declaration is already facing a lawsuit filed by several states—and now, as expected, Democrats are mounting their own challenge to the president’s possibly unconstitutional measure to build his long-sought border wall. In a letter Wednesday obtained by Politico, Nancy Pelosi called on lawmakers to support a resolution by Texas Representative Joaquin Castro seeking to “terminate this emergency declaration.”

“The President’s decision to go outside the bounds of the law to try to get what he failed to achieve in the constitutional legislative process violates the Constitution and must be terminated,” Pelosi wrote to both Democrats and Republicans of the resolution, which, according to the Associated Press, is expected Friday. “We have a solemn responsibility to uphold the Constitution, and defend our system of checks and balances against the President’s assault.”

The unsurprising move comes in response to Trump’s announcement last week that he would go around Congress to fund his border wall between the United States and Mexico. The resolution is almost certain to pass the Democratically controlled House, which would force a vote in the Senate, where several members of the president’s own party have voiced disapproval of the emergency declaration. “I never thought that was a good idea,” Republican Senator Pat Toomey said of the nuclear option last week. “I still don’t.”

If any four Republicans were to defect and back the Democratic resolution, the measure would pass. G.O.P. Senator Susan Collins has already lent her support to the bill on the grounds that Trump’s maneuver “completely undermines” the role of Congress. But the president would almost certainly veto the resolution if it were to pass, and it’s highly unlikely that enough Republicans would chip in to override it.

The best place to stop Trump from funding his “good old fashioned wall” is still, it seems, in court. The legality of Trump’s nuclear option was always dubious, but was further undercut by the president’s own statement during his Rose Garden announcement last week that he “didn’t need to do this”—a seeming admission that the emergency declaration was not in response to an actual emergency. California and other states have filed a lawsuit seeking to block the move, and Democrats are expected to file their own lawsuit soon. Those legal challenges are likely the best hope for those looking to stop Trump’s end around—even if Pelosi and Castro can convince a number of their colleagues to formally condemn his overreach.

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