President Donald Trump doubled down on his assertion to shut down the government if a new spending measure omits his request for billions of dollars in funding for a border wall.

“There will be a shutdown that will last for a very long time,” Trump said in a tweet Friday morning.

Trump later followed up with another brief post, stating, “Shutdown today if Democrats do not vote for Border Security!”

“Even President Ronald Reagan tried for 8 years to build a Border Wall, or Fence, and was unable to do so,” he added in another tweet. “Others also have tried. We will get it done, one way or the other!”

U.S. stock indices, which had already been under pressure following a two-day sell-off, dipped slightly lower following Trump’s comments. But while the prospect of a government shutdown adds uncertainty to already rattled market, historical performance of the S&P 500 following a shutdown could provide some confidence. During the past five shutdowns – two in 2018, one in 2013 and two in 1995 – the S&P 500 (^GSPC) rose during all of them.

House of Representatives Speaker Paul Ryan said on Thursday that Trump would not sign a spending measure if it did not include money for his proposed border wall. The House of Representatives passed a stopgap measure Thursday night to fund the government that includes the $5 billion for the border wall Trump had sought. The vote was 217-185 in favor of the resolution.

However, the Senate on Wednesday night passed a funding bill that does not include money for the border wall. The Senate now must consider the House version of the bill before midnight in order to avoid a potential government shutdown. The bill will require a 60-vote majority for passage.

Trump’s comments come following a heated debate between the president and Democratic congressional leaders last week, during which Trump said he would be “proud to shut down the government for border security.”

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Emily McCormick is a reporter for Yahoo Finance. Follow her on Twitter: @emily_mcck

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