The Senate will be divided 50-to-50 between Republicans and Democrats in the new Congress, giving Democrats control because Vice President-elect Kamala D. Harris will have the tie-breaking vote. Democrats’ 222-to-211 majority in the House is the narrowest for either party in years.

With those margins, even holding enough Democrats together to pass legislation along party lines could prove a challenge. The most conservative Senate Democrat, Sen. Joe Manchin III (W.Va.), has already expressed skepticism about the need for a new round of stimulus checks, while Rep. Alexandria Ocasio-Cortez (D-N.Y.) said Thursday that Biden isn’t going far enough by proposing $1,400 checks, even though Biden’s approach means most people will end up with $2,000 given the earlier batch of $600 checks. “$2,000 means $2,000. $2,000 does not mean $1,400,″ Ocasio-Cortez said.