President Donald J. Trump debates with House Minority Leader Nancy Pelosi, D-Calif., as Vice President Mike Pence listens during a meeting in the Oval Office of White House on Tuesday, Dec. 11, 2018 in Washington, DC.

More investors are feeling jittery about the market. And their No. 1 concern is the political landscape in Washington.

That's according to the latest retail investor sentiment report released by Charles Schwab. The results are based on an online survey conducted in December, before the partial federal shutdown, which began on Dec. 22 and lasted for 35 days.

Lawmakers reached a deal on Friday to reopen the government until Feb. 15. President Donald Trump said over the weekend that another shutdown is "certainly an option."