Minnesota is now ground zero in the 2018 midterm elections

Al Franken's resignation Thursday means the state will now have two Senate seats on the ballot: a special election to fill the last two years of Franken's term, as well as fellow Democratic Sen. Amy Klobuchar's re-election.

The state also features five House races that could swing control of the chamber -- with the seats of two Republicans (Reps. Erik Paulsen and Jason Lewis) and three Democrats (Rick Nolan, Tim Walz and Collin Peterson) all top targets.

Walz isn't even running for re-election. Instead, he's running for governor, to replace the term-limited Democratic Gov. Mark Dayton.

All this comes in a state that was surprisingly competitive in the 2016 presidential campaign: Hillary Clinton bested Donald Trump by just 1.5 percentage points.

Its evolution toward swing state status is part of the remaking of the American political map amid major demographics changes.

Republican strength is growing in the industrial Midwest, with Iowa and Ohio looking increasingly reliable and Wisconsin and Minnesota becoming battlegrounds. Democrats, meanwhile, are increasingly looking to Southern states like North Carolina, Arizona and Georgia.

"Ohio is the new Missouri, Wisconsin is the new Ohio, Minnesota is the new Wisconsin," tweeted Republican ad-maker Brad Todd.

With Franken's resignation, Minnesota -- already crucial to control of the House, where Democrats need 24 seats to regain the majority -- becomes one of 2018's most important states.

It joins California, which features seven Republican-held House seats in districts that Clinton won in 2016 and Democrats are now targeting, as well as a governor's race and state Senate leader Kevin de León's primary challenge to Democratic Sen. Dianne Feinstein.

Also on the list of key states is Arizona, with competitive House races and retiring Republican Sen. Jeff Flake's seat representing one of the few Democratic pickup opportunities of the election cycle.

It's still too early to tell how Franken's resignation will reshape Minnesota's politics.

Dayton will appoint a replacement to fill Franken's seat until the special election, and immediate speculation has focused on Lt. Gov. Tina Smith. But it's not clear whether Smith will get the job -- or if she'd run for re-election or simply be a placeholder.

"Events have unfolded quickly; thus, I have not yet decided on my appointment to fill this upcoming vacancy. I expect to make and announce my decision in the next couple of days," Dayton said in a statement Thursday.

Klobuchar's coattails could help whoever the Democratic governor does appoint: Of the 53 instances in which both of a state's Senate seats have been on the ballot in a single election, the same party has won both seats 45 times, according to the University of Minnesota's Eric Ostermeier.