BREAKING: With Senate short of votes, US government shuts down at midnight 19 January 2018

The key procedural vote needed to advance the short-term spending bill funding the government was short of the 60 votes needed in the Senate late tonight, and the government officially shut down at midnight for the first time since 2013.

Historical data suggests that a big market move shaking stocks is unlikely, but a shutdown would still be concerning to investors.

"Although a government shutdown sounds scary, the reality is it has been a non-event historically for equities," Ryan Detrick, a senior market strategist at LPL Financial, said in an email. "Going back nearly 40 years, the median return during shutdowns has been exactly flat. Not to mention the last shutdown in 2013 saw an impressive 3.1% gain in the S&P 500."

According to the firm’s analysis of S&P 500 performance during government shutdowns dating all the way back to President Gerald Ford in 1976, stocks have seen an average decline of just 0.6% during federal freezes, with 44% of them resulting in gains.

The S&P 500 gained 3.1% during the most recent government shutdown in 2013 under President Obama, and was also positive during the two that happened during the Clinton administration.