President Trump tweeted Thursday afternoon that Defense Secretary Jim Mattis will retire at the end of February.

The move comes amid heightened fears of disfunction in Washington as Trump moves to shut down the U.S. government if funding for a border wall with Mexico isn't included in a stopgap spending bill from Congress this week.

Wall Street saw share prices tumble again Thursday following Wednesday's interest rate hike by the Fed and in the wake of the government shutdown threats.

The announcement of Mattis' departure came just hours after Trump abruptly declared victory over ISIS in Syria and said U.S. troops will be withdrawn from the country.

Mattis was among the longest serving members of Trump's cabinet which has seen frequent turnover during his administration.

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This article was written by a staff member of TheStreet.