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President Donald Trump threatened on Sunday to force a government shutdown if Democrats don’t cave to his demands for stricter immigration policies, including building his long-promised border wall.

“I would be willing to ‘shut down’ government if the Democrats do not give us the votes for Border Security, which includes the Wall!” Trump wrote on Twitter. “Must get rid of Catch & Release etc. and finally go to system of Immigration based on MERIT! We need great people coming into our country!”

I would be willing to “shut down” government if the Democrats do not give us the votes for Border Security, which includes the Wall! Must get rid of Lottery, Catch & Release etc. and finally go to system of Immigration based on MERIT! We need great people coming into our Country! — Donald J. Trump (@realDonaldTrump) July 29, 2018

Congress needs to pass legislation to fund the government by September 30, a task made increasingly difficult as the House has already gone on its summer recess. After members return, they will have only a few days to pass a stopgap spending bill before the start of the next fiscal year. Trump’s tweet raises the stakes for those negotiations, which will come just before the midterm elections and at the same time Senate Republicans attempt to confirm Supreme Court nominee Brett Kavanaugh.

A spending bill released by House Republicans this month allocates $5 billion next year for a border wall. But in the Senate, where Democrats have greater power to block legislation, a bill to fund the Homeland Security Departments includes much less—$1.6 billion.

Sunday morning’s tweet-threat came shortly after another firmly worded tweet showing the president’s neverending anger over immigration:

Please understand, there are consequences when people cross our Border illegally, whether they have children or not – and many are just using children for their own sinister purposes. Congress must act on fixing the DUMBEST & WORST immigration laws anywhere in the world! Vote “R” — Donald J. Trump (@realDonaldTrump) July 29, 2018

If a government shutdown sounds familiar, that’s because it’s already happened this year. In January, as the deadline approached for extending DACA, Democrats demanded the government act to preserve the popular program—which allowed some immigrants who were brought to the United States as children to remain in the country—before they passed a spending bill. The White House increasingly demanded more immigration policies in exchange, and the government shut down. But Democrats soon backed down.

Since then, Trump has repeatedly floated the idea of using a government shutdown as leverage to force Congress to pass hard-line immigration policies: “I’d love to see a shutdown,” he said at a White House meeting on MS-13 in February.