Democrats are almost certain to take over the House in the midterm elections, but Republicans seem likely to hang onto their Senate majority, according to predictions from major poll watchers less than three weeks before the vote.

Election watchers agree that Democrats have a virtual lock on the House, and may even be able to grab a significant majority there.

The Cook Political Report expects Democrats to pick up at least 25 seats, just more than the 23 they need to win control again for the first time since 2010. But Cook says Democrats could pick up as many as 40 seats.

Polling site 270towin has Democrats on the verge of winning at least 208 seats, and some portion of 29 seats considered tossup races. Democrats would only need to win 10 of those tossups to take control.

That assessment is close to that of RealClearPolitics, which has Democrats winning 206 House seats with 30 tossups left.

FiveThirtyEight says the average projected gain for Democrats in the House is 39 seats, and says there's only a 10 percent chance that Democrats gain fewer than 19 seats.

That site also gives Democrats a 10 percent chance of picking up more than 62 seats. There is precedent for such a huge turnaround — Republicans won 63 seats in 2010.

But while the House is seen as a lock, the Senate that Republicans now control by a slim 51-49 majority seems likely to remain in control of Republicans.

Democrats are protecting 26 seats this time around, and the Cook Political Report says five of them are tossups: Nelson of Florida, Donnelly of Indiana, McCaskill of Missouri, Tester of Montana, and Heitkamp of North Dakota.

Republicans are only defending nine seats, but four of those are tossups: Heller of Nevada, Cruz of Texas, the open seat in Arizona due to Sen. John McCain's death, and the open seat in Tennessee due to Sen. Bob Corker's retirement.

270towin says 49 Republicans are on the verge of winning, which means Republicans need just one of the remaining seven tossup races to maintain control. RealClearPolitics puts it at 50 GOP seats plus six tossups.

FiveThirtyEight says Republicans have an 80 percent chance of keeping control of the Senate.