Since Donald Trump was elected president, Democrats have been counting on an energized liberal base to send a big, blue wave to wipe out Republican congressional majorities this November.

But less than a month away from the midterms, some Democrats are concerned their party may be more confident than they should be about retaking control of one or both chambers – amid a tightening electoral map.

For some, they’re recalling memories of the 2016 presidential election, when a Hillary Clinton victory was long assumed as inevitable, only for her party's hopes to be dashed.

“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.”

Al Sharpton, the liberal cable news host who ran for president as a Democrat in 2004, said Democrats shouldn’t take anything “for granted” ahead of next month's vote, citing what happened in 2016.

“I think that if they just look at the polls and relax, they will end up having the same result they had in '16 when every Democrat I know were already planning what they were wearing to Hillary Clinton's inauguration and we never got there,” Sharpton said last week on MSNBC.

Among concerns are that Democrats have focused in recent months on longshot Senate bids to derail Republican candidates in reliably red states instead of more winnable Midwest battlegrounds.

Democrats have poured money and energy into places like Texas, where Democratic Rep. Beto O'Rourke raised more than $38 million last quarter in his bid against incumbent Republican Sen. Ted Cruz. They’ve also had high hopes in Tennessee, where centrist former Democratic Gov. Phil Bredesen is running against conservative Rep. Marsha Blackburn.

Polling now suggests O'Rourke's momentum has flatlined, as a Quinnipiac University poll released Thursday showed O'Rourke trailing Cruz by 9 points. In Tennessee, Blackburn has surged to a double-digit lead, even as Bredesen won the endorsement of music superstar Taylor Swift.

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"Liberal activists and online media [are] touting Democratic chances and paying more attention to stretch cases like Texas and Tennessee, when the Democrats need to protect vulnerable incumbents in states like Missouri and Indiana," Michigan State University political science professor Matt Grossman recently told Fox News.

"That reminded me of talks about possible Democratic wins in Arizona, Georgia, and Texas in 2016, when Clinton had to protect the Midwest states," he added.

Republicans have called it a blessing that donors have sent money to Texas, rather than places like Missouri or Indiana, where Democratic incumbents are locked in tight contests.

“How nice that Beto is draining the resources of left-wing donors across the country for a race he’s sure to lose, while that money could have gone into tight races that Democrats have a fighting chance to win,” conservative commentator Dinesh D’Souza said.

According to the Fox News Senate Power Rankings, Democrats have the edge for at least 45 seats (including seats not up for election, or ranked likely or lean Democrat in elections this cycle), while Republicans have the advantage for at least 50 seats.

Remaining are five seats considered tossups. They are in Florida, Indiana and Missouri – where Democrats are defending seats – and Nevada and Arizona where they hope to flip a seat. In other competitive races, Democratic incumbents in West Virginia and Montana are polling slightly ahead of their Republican challengers, though North Dakota incumbent Sen. Heidi Heitkamp is trailing her Republican rival.

Fifty-one seats are needed for a majority.

Meanwhile, Democrats are still seen having a much better shot at winning a majority in the House. According to the Fox News Power Rankings, 207 House seats are likely or lean Democrat, while 197 seats are likely or lean Republican. There are 31 toss-up seats. It takes 218 seats to have the majority.

The political environment still favors Democrats, as the party of the president typically loses seats in midterm elections. Democrats hold an 11-point lead on Republicans on a generic congressional ballot, according to a Washington Post/ABC News poll.

But Republicans say the recent brutal fight over now-Justice Brett Kavanaugh’s Supreme Court confirmation has energized the base and could blunt the expected Democratic romp in House races.

“Something incredible has happened over the last couple of weeks. And that’s called the 'Kavanaugh effect' on Republican voters," former White House chief of staff Reince Priebus said in a weekend radio interview on AM 970 in New York.

Other Republicans say it’s possible the GOP even keeps control of the House.

"If, over the next three weeks, they keep those Trump voters engaged, we have a shot at holding the House," GOP pollster John McLaughlin said on John Catsimatidis’ radio show.

“I don't think the Democrats take back the House,” outgoing Pennsylvania GOP Rep. Ryan Costello said Sunday on MSNBC. “I've not seen data that shows they're going to do that. Obviously, the generic ballot says what it says, but I think right now they pick up a dozen seats or so. There's three weeks to go here. So things could change but I don't see a blue wave.”

Others have cited Democratic antics during Kavanaugh’s confirmation battle and the uptick in confrontational tactics by liberal protesters (and comments egging them on by former presidential candidate Hillary Clinton and former Attorney General Eric Holder).

“Much of this is now making its way into the GOP’s ad campaign for the midterms,” Bret Stephens, a New York Times conservative columnist, wrote in a recent column. “That’s natural because the left has given Republicans so much material to work with.”

Still, despite the anxiety from some in the party, other Democrats remain optimistic.

“Democratic energy is at nuclear levels,” Steve Israel, the former Democratic Congressional Campaign Committee chairman, told McClatchy. “Democrats would crawl over broken glass to vote in this election.”

Fox News’ Gregg Re contributed to this report.