A likely rematch of Brown's 2012 victory over state Treasurer Josh Mandel will be fought on altered terrain. That year, Brown appealed to the same blue-collar voters that embraced Trump in 2016. Mandel, meanwhile, has spent the past six years making as many enemies as allies in GOP politics: He endorsed Florida Sen. Marco Rubio over his home-state governor, John Kasich, and hasn’t endeared himself to Republicans in Washington. If he defeats businessman Mike Gibbons in the primary, Mandel, a strong fundraiser, will have the money to challenge Brown across Ohio’s expensive television markets.
Indiana's Senate race cracked the top 3:
3. Indiana — Democratic Sen. Joe Donnelly running for reelection
Donnelly, like McCaskill, is running for reelection in a state Trump won handily. But while McCaskill is already locked in to a one-on-one matchup with Hawley, Donnelly will get to watch three different GOP primary contenders — Reps. Todd Rokita and Luke Messer, along with self-funding businessman Mike Braun — beat up on each other until the primary in May. Republicans believe they landed a major hit on Donnelly when the Associated Press reported he profited from a family company outsourcing jobs to Mexico. Donnelly sold his stock in the company after the story was published.