History, demographics and the national mood are pointing to one conclusion about the 2018 congressional races: Democrats are well-positioned to bring one-party government in Washington under Donald Trump’s presidency to a screeching halt.

There’s a confluence of evidence indicating a so-called wave election may be building that would allow Democrats to wrest the House of Representatives from Republican control. A Democratic takeover of the Senate will be harder to achieve.

“We are all very sensitive to the political environment we’re in,” said Oklahoma Representative Tom Cole, who led House Republicans’ campaign arm in 2008. Republicans are girding for an “extraordinarily competitive” election.