As House Minority Leader Nancy Pelosi confidently predicts victory in next week's midterms, at least one major political oddsmaker is giving her a boost: Cook Political Report is now saying Democrats could win as many as 40 seats in the House.

Dave Wasserman, House editor of the nonpartisan Cook Political Report, tweeted late Wednesday that the unit is revising its outlook to reflect a Democratic gain of 30-40 seats, up from 25-35. He warned that the outlook could change again before Tuesday.

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Even some in Pelosi's party are cautious about the pitfalls of overconfidence, amid recent reports of veteran operatives warning that the curtain-measuring echoes Democrats' confidence in the lead-up to the 2016 election, which now-President Trump won.

Talk show host Stephen Colbert said as much when Pelosi predicted on his show earlier this week, "We will win." She is expected to seek the speakership again if she's right.

“Do you want to say that on Hillary’s fireworks barge that she canceled?” Colbert shot back, referring to Hillary Clinton’s planned fireworks for the night of her expected 2016 presidential victory. “Please don’t say that.”

Fox News’ Power Rankings reflect a strong Democratic advantage in the race for the House, but not a lock. The ratings show 207 seats tilting toward the Democrats and 199 tilting toward Republicans, and the rest up in the air. It takes 218 seats to claim a majority. The Real Clear Politics map shows 204 House seats tilting Democratic, and 199 tilting Republican, with 32 in the “toss-up” column.

Fox News’ media analyst Howard Kurtz cautioned Wednesday about getting carried away by “blue wave” predictions.

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“While the odds are against the Republicans, they probably have a better shot at holding the House than Trump appeared to have two years ago in the Electoral College,” he wrote. “And if the Democrats do gain control, will it be by winning barely more than the 23 seats they need, or by the 30 or 40 seats that would constitute a blue wave?”

“Election Day will either prove to me I have PTSD or show I’ve been living déjà vu,” former Clinton spokesman Jesse Ferguson told McClatchy about the upcoming elections. “I just don’t know which yet.”

In the Senate, Republicans retain the edge, but a number of races are well within the margin of error, making the predictions fuzzy. A new round of Fox News battleground polls shows three of five key Senate races could go either way -- races that will determine which party holds the chamber.

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Candidates are tied in Arizona and Missouri, while Republicans are holding comfortable leads in Tennessee and North Dakota. In Indiana, incumbent Democratic Sen. Joe Donnelly is leading Republican challenger Mike Braun by 7 points, but 9 percent of voters are still undecided.

Arizona is an example of how wildly fluctuating polls can be. Fox News' poll found the race between Republican Martha McSally and Democrat Kyrsten Sinema tied, while an ABC 15/OH Predictive Insights poll put McSally ahead by 7.

The Fox News Power Rankings puts 50 Senate seats in the Republican column (including those likely or leaning Republican, and GOP seats not up for election this year), and 45 in the Democratic column. Five races are marked as "toss-ups."

Fox News' Brooke Singman contributed to this report.