ST. PAUL (AP) -- Democratic U.S. Representative Rick Nolan says he will retire to spend more time with family, creating an open race for a northeast Minnesota House district that has become swing territory in the past decade.

Nolan says he's stepping aside to give other 8th District candidates plenty of time to build campaigns. He already faced at least one primary challenger.

The 74-year-old Nolan barely defeated a Republican challenger in his two re-election bids in 2014 and 2016. The sprawling district was among the most expensive congressional races in the country.

Nolan has struggled to bridge pro-mining factions on the Iron Range with more liberal and environmentally conscious Democrats who have sought to block new mining projects.