President Trump and House Speaker Paul D. Ryan (R-Wis.). (Evan Vucci/AP)

Cook Political Reports tells us:

If it wasn’t already clear, last Tuesday’s election results confirmed a political atmosphere that would seriously endanger the House GOP’s majority in 2018. In Virginia, turnout was up 20 percent over 2013 in localities won by Hillary Clinton, compared to 13 percent in localities carried by President Trump. Not only did Democrat Ralph Northam outperform pre-election polls, Democrats shocked by nearly winning control of Virginia’s House of Delegates. …

Republicans held onto just two of their 17 seats in districts Clinton carried, and are headed to a recount in a third. The results suggest Northern Virginia Rep. Barbara Comstock (VA-10) is the single most vulnerable GOP incumbent in the country.

Earlier in the year, Democrats went into a funk at the time over four special House elections, but Cook’s take is that their performance in them was overall a positive sign. “Democrats outperformed Clinton anywhere from one point (GA-06) to 13 points (KS-04), [and] the balance of evidence suggests Democrats would be the ever-so-slight favorites to reclaim the House if the elections were held today. New congressional generic ballot polls showing Democrats with double-digit leads only bolster that assessment.”

Cook is careful to remind us that the elections are a year away and scandal and retirements could take down more incumbents. However, it’s also very possible the climate gets worse for Republicans. A special counsel report, the failure of the tax bill (or passage of a strongly disliked tax bill), or a stock market blip could make for an even worse midterm election for the House GOP.

By changing ratings in 7 races (6 to favor Democrats), Cook leaves Democrats with more than four dozen competitive possibilities. Among the toss-up-or-worse seats, Republicans have 18 at risk, and Democrats have only 4. In the “leans”/”likely” category, Republicans have 45 seats that aren’t entirely solid. Democrats have 16. (If you separate out just the “lean” seats, Republicans have 20 at risk while Democrats have only 5.)

The Washington Post readers are some of the most critical out there. Opinion writer Jennifer Rubin reads and responds to her hate mail from both sides of the aisle. (Adriana Usero,Kate Woodsome/The Washington Post)

Over in the Senate, it’s not likely but certainly possible Democrats take the majority. It is increasingly likely that Doug Jones will win the Alabama seat, narrowing the GOP majority to 51-49. If the two most vulnerable Republican seats flip (Nevada and Arizona) and red-state Democrats hold on (Missouri and Indiana are the most vulnerable), Sen. Mitch McConnell (R-Ky.) and his Republicans are back in the minority.

If the Democrats take one if not both houses, Republicans and President Trump specifically should panic. With majorities come control of committee oversight and subpoena power. The filibuster would remain to block Democratic-sponsored legislation, but one could image Sen. Charles E. Schumer (D-N.Y.) rounding up a number of Republican votes (Shelley Moore Capito of West Virginia, Lisa Murkowski of Alaska, Susan Collins of Maine, John McCain of Arizona, Cory Gardner of Colorado, Steve Daines of Montana, etc.) on health-care or infrastructure measures while more-generous immigration legislation along the lines of the Gang of Eight (which passed the Senate) could get through both bodies.

It is, however, the prospect of impeachment (if not removal) that would most alarm the White House. While it seems exceptionally unlikely that President Trump would be removed from office (two-thirds of the Senate would be required to vote for removal), by that point, Trump’s presidency could well be in shambles with the 2020 election looming.

In short, despite their shellacking in 2016, Democrats have a reasonable chance of staging a rather quick comeback in Congress and in state races (Republican governors will be defending in 26 states, some in blue states such as Illinois, Maine and Maryland). Former president Barack Obama, fairly or not, is blamed for hollowing out the Democratic Party; Trump could do the same for Republicans.