Most national polls show Americans preferring Democrats over Republicans in the mid-term congressional elections by 10-18 percentage points, though the margin has narrowed in some recent polls. Republicans and Democrats alike are giving extra attention to a a few Senate seats in particular.

Why it matters

The president's party traditionally takes a hit in his first midterm, and Democrats only need 24 House seats and two Senate seats to win majorities in both. But the odds are low that the Senate would change hands, since 10 Democratic senators are up for re-election in states Trump won. It's also worth watching to see if the polls change after the debacle over the government shutdown.

Big picture

Democrats are hoping to flip seats in Nevada and Arizona, the former of which voted for Hillary Clinton in 2016. Enthusiasm is high after important wins in 2017 in New Jersey, Virginia and Alabama and national disapproval of President Trump.

are hoping to flip seats in Nevada and Arizona, the former of which voted for Hillary Clinton in 2016. Enthusiasm is high after important wins in 2017 in New Jersey, Virginia and Alabama and national disapproval of President Trump. Republicans are targeting 10 Democratic senators up for re-election in states that Trump won in 2016 — including five he won by double digits: Missouri, North Dakota, West Virginia, Montana and Indiana. Republicans have the financial and structural edge over Democrats, having raised even more money than in 2016.

States to watch

Democratic hopefuls:

Nevada: Democratic Rep. Jacky Rosen will most likely run against incumbent Republican Dean Heller, who has been almost unanimously named the most vulnerable Republican in the 2018 midterms after flip-flopping on GOP's health care bills — opposing the original proposal to repeal the Affordable Care Act, but voting in favor of the "skinny" repeal. Arizona: With the highly unpopular Jeff Flake out of the race and Arizona only narrowly voting for Trump in 2016 (49%-45%), Democrats are hopeful that Rep. Krysten Sinema can take the seat. She's likely to face either Rep. Martha McSally or Kelli Ward, who will compete in the Republican primary. (Ward has recently been attempting to distance herself from Steve Bannon, who had been supporting her run.) Tennessee: Republicans see this seat as safe, especially with Trump's decisive victory there in 2016. But since Sen. Bob Corker announced his retirement, Democrats are eyeing it as a potential third seat in play, with former governor and Nashville mayor Phil Bredesen as their likely candidate.

Republican hopefuls — all states Trump won in 2016: