Signs of a blue wave are increasing as lawmakers return to Washington for their final few weeks of legislative work before the crucial midterm elections.

Democrats have led Republicans by at least 11 points in five of the last six polls asking voters whether they favor a generic Democrat or a generic Republican in the race for Congress.

That margin only slightly trails the Democratic advantage in 2006, when the party won back control of Congress.

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Democrats also enjoy a fundraising advantage, one that is perhaps bolstered by polls showing their party is more enthusiastic about turning out to vote this November, figures borne out by higher turnout in Democratic primary contests in states across the country.

After a brutal August that ended with the conviction of his former campaign chairman, a guilty plea from his former personal lawyer and a final feud with Sen. John McCain John Sidney McCainCindy McCain endorses Biden: He's only candidate 'who stands up for our values' Biden says Cindy McCain will endorse him Biden's six best bets in 2016 Trump states MORE that played out during memorials to the late Arizona Republican, President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE’s job approval rating has sunk to record or near-record lows in several polls.

Reputable surveys show his approval rating trading at the nadir of his traditional range, between 36 percent and 41 percent. More voters strongly disapprove of Trump than approve in total, a measure of how heavy an anchor he will be around the GOP candidate’s necks.

Taken in total, the evidence suggests the Labor Day holiday may have been the point where the blue wave crested for Democrats — at least when it comes to the battle for the House.

As recently as late July — 100 days out from the midterms — signs of the wave were much less evident.

Republicans take solace in a Senate map that bolsters their chances of growing a narrow majority, though Democrats also hope to break through and win the Senate majority.

And those tasked with maintaining control of the House say they remain optimistic.

“We’re going to wake up and run every day as if we’re down 10 points. We’re leaving nothing to chance. But we’re confident with our great candidates who are talking about the issues that actually matter to voters, we’re going to defy history,” said Matt Gorman, a spokesman for the National Republican Congressional Committee.

But a wide variety of data suggests Republicans face strong headwinds in retaining their House majority.

The number of House districts rated as potentially vulnerable to a party flip by the nation’s top elections analysts is growing, and most of these competitive seats are held by Republicans.

The Cook Political Report calls 41 seats “toss-ups or worse,” with only three held by Democrats. Sabato’s Crystal Ball rates 45 seats similarly, with three held by Democrats. Nathan Gonzales at Inside Elections rates 86 seats as in play, only 10 of which are held by Democrats.

Democrats running for House seats have raised $621 million this year, compared with $470 million for Republicans, according to tallies of Federal Election Commission filings by the Center for Responsive Politics. Democratic candidates for Senate seats have raised $368 million, compared with $258 million for the Republicans running for those same seats.

By comparison, Republican House candidates outraised Democrats by $140 million in 2014, and Senate Republicans outraised Democrats by $40 million.

The most recent national polls show almost nothing but doom and gloom for the GOP. Surveys conducted over the last two weeks by Suffolk University on behalf of USA Today and TIPP for Investor’s Business Daily show Democrats leading the generic House ballot by 11 points; Reuters/Ipsos and Emerson College polls peg the Democratic advantage at 13. The pollsters at ABC News and The Washington Post put the edge at 14 points.

Dig beyond the toplines and the numbers are even starker. Democrats lead among independents by 14 points in the Emerson survey, and by 18 points in the ABC/Washington Post poll. In another measure of up-for-grabs voters, self-described moderates backed Democrats by 30 points in the ABC/Post poll, and by 21 points in the Economist/YouGov survey — the only survey that showed Republicans within single digits among all registered voters.

Asked whether voters prefer a Democratic Congress that acts as a check on Trump or a Republican Congress that backs his agenda, 60 percent of those interviewed by ABC and the Post opted for a Democratic check. The USA Today/Suffolk poll found 58 percent wanted a Democratic Congress to stand up to Trump, versus just 34 percent who wanted a Republican Congress that mostly cooperated with the White House.

Those are wider than the margins by which voters favored a Republican Congress to stand up to former President Obama in 2010, just weeks before Republicans won back 63 seats and control of the House.

Polls may be criticized for their sample sizes or voter screens, but actual election results carry no margins of error. Democrats have inarguably overperformed in a series of special elections since Trump was inaugurated, flipping a U.S. Senate seat, a House seat and nearly two dozen GOP-held state legislative seats, some in deep-red territory like Oklahoma, Missouri and Wisconsin.

Primary elections, too, have showed Democratic voters are more enthusiastic about voting this year. Of the 42 states that have held primaries so far this year, more Democrats have showed up to vote than in 2014 in 35, compared with 30 states where more Republicans showed up to vote. The average Democratic turnout is up 64 percent, while the average Republican turnout in those states is up 38 percent over 2014 levels.

A month ago, the publicly available data showed Democrats with an advantage, however marginal. Nine weeks before voters head to the polls, that advantage is growing substantially.