CHICAGO — Scientist Sean Casten emerged from a crowded field to win the Democratic primary and a chance to challenge Illinois Republican U.S. Rep. Peter Roskam in November.

Roskam, who represents a largely white district covers suburbs north and west of Chicago, was unopposed in the GOP primary on Tuesday.

Democrats have made capturing Roskam’s seat a priority in their efforts to regain control of the House. Roskam took heat last year for supporting the repeal of the Affordable Care Act. Democrats are also counting on frustration with President Donald Trump’s policies.

Casten defeated Kelly Mazeski, who has held a municipal office and had the fundraising in the race. Others running were Amanda Howland, attorney Jennifer Zordani, data analyst Ryan Huffman, bookstore owner Becky Anderson Wilkins and attorney Carole Cheney.