The composition of the current Senate is 52 Republicans, 46 Democrats and 2 Independents (who caucus with the Democrats). The Democratic caucus must hold at least 41 seats after the 2018 election in order to defeat the passage of legislation by filibustering. Since there are only 8 Republican held seats up for reelection and 25 Democratic or Independents seats, the 2018 Senatorial election will require much greater public support for the Democratic caucus to hold enough solid seats to successfully filibuster the damaging legislation based upon the Republican Party platform.
If the resistance movement can grow large enough, it may in fact yield Democratic gains in the Senate and the House in 2018.
Voter turn out was extraordinarily low in the 2016 election - much greater public engagement gives hope for greater Democratic voter turnout in 2018.
Angus King (I)
Bob Casey, Jr.
*Indicates that, at this time, this seat could be difficult for Democrats to win.
**Indicates that, at this time, this seat could be particularly difficult for the Democrats to win because Trump carried the state by double digits.