Wall Street's main indices have closed lower as investors took some profits after last weeks' record levels while they waited for earnings season to begin and eyed events in Washington with trepidation.
US stocks had rallied last week as investors bet that Democrats' win of Georgia run-off elections would bring a higher likelihood of a heftier fiscal stimulus package to boost the pandemic-savaged economy.
But some investors worried stimulus could be delayed as House Democrats introduced a resolution to impeach US President Donald Trump, accusing him of inciting insurrection following a violent attack on the Capitol by his supporters.
"When markets are looking at something as critical as the governance of the United States, even a little bit of uncertainty can have a meaningful impact," said Brad McMillan, chief investment officer at Commonwealth Financial Network in Waltham, Massachusetts.
McMillan said investors also worried about more attacks.
"Generally speaking, Washington doesn't make too much of a difference but since policy is influencing so much of what's expected around the economy, this is kind of a unique time," he said.
But with US Treasury yields rising on Monday and outperformance of economically-sensitive sectors such as energy and financials, Keith Lerner, chief market strategist at Truist Advisory Services in Atlanta, Georgia, said investors were still hopeful about stimulus.
"After last week the market is in a little bit of a digestion phase. Underneath the surface what you're seeing continue is the reflation trade," said Lerner. "This is a continuation of the expectation of more fiscal stimulus."
And along with wariness about Trump's last nine days in office, Lerner also cited uncertainty before the unofficial start of earnings season on Friday when banks such as JPMorgan report results.
Unofficially, the Dow Jones Industrial Average fell 0.29 per cent to end at 31,008.69 points, while the S&P 500 lost 0.66 per cent to 3,799.61.
The Nasdaq Composite dropped 1.25 per cent to 13,036.43.
Shares of the micro-blogging site Twitter Inc tumbled after it permanently suspended Trump's account. But it shares were still about 160 per cent higher that where they traded before Trump won the Presidential election in 2016.
Facebook Inc, Alphabet Inc-owned Google and Apple Inc were also weak on Monday as they took their strongest actions yet against Trump to limit his social media reach.
Investors are expecting guidance on the extent to which executives see a rebound in 2021 earnings and the economy from results and conference calls from JP Morgan, Citi and Wells Fargo Friday.
Boeing Co fell on Monday after a 737-500 jet operated by Indonesia's Sriwijaya Air with 62 people on board crashed on Saturday.
However, shares in Eli Lilly and Co rose sharply on Monday after a small trial of its experimental Alzheimer's drug found that it slowed by about a third the rate of decline in a combined measure of cognition and function in patients at an early stage of the disease.