MINNEAPOLIS — Political operatives in Minnesota and Washington were drawing up lists of candidates to run for Sen. Al Franken’s Senate seat even before his resignation speech last week, searching for prospects with the profile, fundraising prowess and mettle to sprint to next November’s special election — and then do it again in 2020 to hold the seat for six more years.

Franken’s decision to quit in a sexual-harassment scandal has scrambled Minnesota’s 2018 election, which was already on track to be the most high-stakes political cycle in the state in years. The looming battle for control of the U.S. House could run through up to five competitive races in Minnesota, and an open governor’s race puts Republicans in a position to take full control of state government for the first time in half a century.

No one has declared for the new Senate race yet, but many big names are in the mix. Democratic-Farmer Labor Lt. Gov. Tina Smith and former Republican Gov. Tim Pawlenty are among those being discussed, but both parties will consider a half dozen or more possible contenders. Smith, seen as Gov. Mark Dayton’s likeliest choice as Franken’s immediate replacement through the special election, has emerged as a possible candidate for the long term.

“Anyone who gets in will need to demonstrate an ability to organize quickly, fundraise and create a campaign to go the distance, and the distance is 2018 and then again in 2020. That will be a deterrent,” said Doug Loon, president of the Minnesota Chamber of Commerce. Spending on contested U.S. Senate races reaches into the tens of millions of dollars.

Republicans say fears about losing ground in the first midterm election under a new president of the same party — disastrous for the president’s party in 1982, 1994 and 2010 — are alleviated in a special election.