The RNC's Twitter account has used the phrase dozens of times since Biden's inauguration, including in January, when it tweeted: "It is officially election year! Republicans are ready to sweep this November. #RedWave."

Results of polling of voters about a generic ballot, asking which party they'd like to see control Congress without mentioning specific candidates, now show Democrats with a half-point lead, according to FiveThirtyEight. That's a dramatic shift, as Republicans had held a steady two-point lead on the generic ballot since January.

Democrats have outperformed Biden's 2020 margins in recent special House elections, which FiveThirtyEight says is a sign that the "national political environment right now actually leans toward Democrats."

Democrats' surge in the polls has led election forecasters to scale back their predictions of a Republican wave in November.

FiveThirtyEight now predicts that Democrats have a 66 percent chance of controlling the Senate after the midterms. That's a dramatic shift from June, when it said Republicans had a 60 percent chance of winning control of the Senate and Democrats had a 40 percent chance.

The Cook Political Report called its August 24 article on recent special election results "Red Wave Looks More Like a Ripple" as it downgraded its forecast to a GOP pickup of 10-20 House seats instead of its previous prediction of 20-35 seats.

"In May, @CookPolitical's House outlook was a GOP gain of 20-35 seats. Based on recent developments, we've revised our outlook to a 10-20 seat GOP gain, w/ Dems maintaining control not out of the question," Cook Political Report analyst Dave Wasserman tweeted.

CBS News also scaled back its forecast of a red wave, saying Republicans have had "a tumultuous summer" that has made their advantage appear a little smaller today, trending toward narrow gains instead of a wave.

Observers say Democrats have seen their fortunes rise recently for a number of reasons.

They say the Supreme Court's ruling in Dobbs v. Jackson Women's Health Organization that overturned Roe v. Wade's affirmation of a constitutional right to abortion in the United States dramatically shifted the landscape.

And they note a rise in President Joe Biden's approval ratings since Democrats passed the Inflation Reduction Act and following a drop in gas prices.