Democratic primaries in six GOP-held districts saw a roughly 100 percent increase in voters compared to 2016, according to a POLITICO analysis of turnout data. The spike indicates that a lethal recipe might be brewing for Republicans in the run-up to November: President Donald Trump’s unpopularity in the suburbs, combined with rapid demographic change and an amped-up Democratic base.

After coming tantalizingly close to flipping several red-leaning seats in 2018, Democratic candidates are gearing up in and around the state’s five largest cities. Their game plan: win over moderates and independents repelled by the president, and bring in as many new Democratic voters as possible.

Democrats are targeting seven Republican-held districts, though it’s more likely that three or four are truly in play right now. The implications are huge for the congressional landscape: If Democrats seriously contest a half-dozen seats, Republicans will have to spend millions protecting once-safe districts in major media markets, minimizing their odds of taking back the House.