The main impact has been to reinforce what was already the central issue in U.S. politics: “Donald Trump, pro or con?” Now more than ever, opposition to Trump defines what it means to be a Democrat and support for him defines what it means to be a Republican.

Support for impeachment rose from 71.9 percent among Democrats the day before Pelosi’s Sept. 24 announcement to 86.3 percent today, whereas Republican support for it has hardly budged, according to the FiveThirtyEight average of polls…

And there is little sign of major losses for Democrats next year, let alone that the House is at risk. The party holds a 5.8 percentage point edge in the “generic ballot” for House races in 2020, according to FiveThirty­Eight, down only modestly from the 8.6 point margin by which they beat Republicans in 2018.

At the presidential level, meanwhile, impeachment has done essentially nothing to Trump’s standing with the public. The day before Pelosi announced the inquiry, 43.3 percent of registered or likely voters approved of the job he was doing; 43.9 percent approve today, while the share disapproving, now 52.1 percent, represents a 1.2 point drop since the eve of her announcement.