Democrats are facing a cash crunch as they seek to go on offense in Senate races that suddenly appear competitive.

Some senior Democratic aides and strategists believe they have a historic opportunity to win as many as nine or 10 Senate seats in November because of the vicious infighting within the GOP over presidential nominee Donald 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.

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But winning big on Election Day, and building what some aides are calling a “seawall” to protect the expected Democratic majority in the 2018 midterm election, won’t be easy — or cheap.

It would require winning seats in states like Florida, Ohio, Arizona and Georgia, where Republicans have long been seen as having the advantage.

Senate Democratic leaders have to decide whether they should try to expand the map beyond the eight battlegrounds they’re now focused on, and even if they go big, they have to figure out where to get the extra money from.

“What happens in wave years, it’s not necessarily that people break decisively to one side — it’s that one side is so disgusted and exhausted they just stay home,” said a senior Democratic aide. “It seems we’re ripe for that.”

But a big wave in Senate races is less likely to happen if Democrats have funding parity in only the most competitive states: New Hampshire, Pennsylvania, Indiana, North Carolina, Nevada and Missouri.

Democrats expect to pick up Republican seats in Illinois and Wisconsin easily

One option for expanding the map is to press Democratic presidential nominee Hillary Clinton Hillary Diane Rodham ClintonButtigieg stands in as Pence for Harris's debate practice Senate GOP sees early Supreme Court vote as political booster shot Poll: 51 percent of voters want to abolish the electoral college MORE's campaign and network of donors for more help. The other is to lean on veteran Democratic senators who aren’t up for reelection or facing little danger this year to give generously from their campaign accounts.

Polls showed the Senate races in Arizona and Ohio in a dead heat earlier this year, but the Republican candidates, bolstered by heavy spending from outside groups, have since pulled ahead.

In Florida, Rep. Patrick Murphy, the Democratic challenger, was a highly touted recruit, and Republican Sen. Marco Rubio Marco Antonio RubioOvernight Defense: Pentagon redirects pandemic funding to defense contractors | US planning for full Afghanistan withdrawal by May | Anti-Trump GOP group puts ads in military papers Democrats step up hardball tactics as Supreme Court fight heats up Press: Notorious RBG vs Notorious GOP MORE hasn’t been able to poll above 50 percent — a serious red flag for any incumbent.

But Rubio, thanks in part to a tremendous Republican spending advantage, opened up a 7-point lead last month and appeared to be cruising to reelection.

Republicans are on track to outspend Democrats in Florida, Ohio, Arizona and Georgia by a combined total of $55 million to $26 million, counting media buys going back to Aug. 31, according to a GOP strategist who tracks advertising.

Those figures include money spent in September and October as well as media reservations up until Election Day.

In Florida, going back to Aug. 31, Rubio, the National Republican Senatorial Committee (NRSC) and outside Republican-allied groups are on track to spend $30 million up until Election Day.

Democrats are on track to spend $14 million, but Florida Democrats estimate that their side will end up spending much less because they expect there to be additional advertising cancellations by Democratic groups.

Since Aug. 31, Republicans have spent a total of $16 million on the Florida Senate race and Democrats have spent only $5.8 million, according to a Democratic strategist who tracks media buys.

An NBC/Wall Street Journal poll from early October showed Rubio ahead of Murphy by only two points, 48 percent to 46.

A more recent University of North Florida poll showed Rubio leading Murphy, 48 percent to 41, but still below the crucial 50 percent mark.

Murphy may get some help from Clinton’s network of supporters. Priorities USA, a pro-Clinton super PAC, launched a new ad in Florida this week with footage from the recently uncovered 2005 tape in which Trump makes lewd comments about how he can treat women however he wants, including grabbing them by the genitals, because he is a celebrity.

Senate Democratic strategists, however, would like Clinton’s allies to make more of an effort to tie Trump to Rubio, who condemned Trump’s comments but hasn’t withdrawn his endorsement.

In Arizona, Republicans — including incumbent 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, the NRSC and outside groups — are on track to spend $3.9 million, counting from Aug. 31. Total Democratic spending will amount to $1.7 million, according to the GOP source who tracks media buys.

An Emerson College poll released last week showed McCain ahead of his Democratic challenger, Rep. Ann Kirkpatrick Ann KirkpatrickArizona Rep. Tom O'Halleran wins Democratic primary Arizona Rep. Ann Kirkpatrick wins Democratic primary Cook shifts 20 House districts toward Democrats MORE, by 15 points.

But McCain’s approval rating is below 50 percent, which puts him in the danger zone if there’s a Democratic wave.

McCain has withdrawn his support for Trump, which may help him attract independent and female voters. But it could also erode his support from pro-Trump voters. Trump lashed out at McCain on Twitter as “foul mouthed” and criticized him for disloyalty after Trump backed him in the GOP primary.

Alexis Tameron, the state Democratic Party chairwoman, says Democratic leaders in Washington “should be re-evaluating Arizona.”

Tameron managed Democratic candidate Richard Carmona’s 2012 Senate bid and argued a late spending surge by Republicans made the difference in that race.

“There was a late surge of spending on behalf of the Republican, Jeff Flake Jeffrey (Jeff) Lane FlakeJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden Maybe they just don't like cowboys: The president is successful, some just don't like his style MORE, and it turned the tide because we rested on our laurels in terms of investing and spending in Arizona,” she said.

Flake, now Arizona’s junior senator, edged Carmona by 3 points.

In Georgia, Republicans are on track to outspend Democrats $2.8 million to $640,000, looking at the period between Aug. 31 and Election Day, according to a GOP strategist who tracks media buys.

Since the end of August, Republican spending on the Senate race has totaled $888,000 and Democratic spending has totaled $592,000, according to the source.

A JMC Analytics poll conducted from Sept. 20 to Sept. 22 showed incumbent Sen. Johnny Isakson Johnny IsaksonLoeffler paints herself as 'more conservative than Attila the Hun' in new campaign ad Georgia GOP Senate candidates cite abortion in pushing Ginsburg replacement Loeffler: Trump 'has every right' to fill Ginsburg vacancy before election MORE (R-Ga.) ahead of Democratic candidate Jim Barksdale, but Isakson's numbers are weak.

Only 36 percent of respondents said they supported Isakson’s reelection, while 38 percent were undecided.

Although Democrats had high hopes for former Gov. Ted Strickland in Ohio, and polls showed him deadlocked with Senate Republican incumbent Rob Portman Robert (Rob) Jones PortmanMcConnell locks down key GOP votes in Supreme Court fight Romney undecided on authorizing subpoenas for GOP Obama-era probes Congress needs to prioritize government digital service delivery MORE earlier this year, a deluge of spending from pro-GOP groups may have buried Democratic hopes beyond rescue.

Two polls conducted since Trump’s video bombshell became public and released Thursday show Portman with a big lead. An NBC/Wall Street Journal poll conducted from Oct. 10 to 12 showed Portman up 18 points.

An Emerson College poll shows Portman up 17 points.

But Strickland and his allies think they can close the gap if GOP voters stay home because of anger over Trump or Portman for withdrawing his endorsement.

Strickland campaign spokesman David Bergstein says the Trump video and the Republican civil war it has caused is likely to have a powerful impact on voter turnout next month.

“Different elements of a potential Republican coalition are alternatively furious at Senator Portman or turned off by Trump’s behavior, while Democrats are more energized than ever before,” he said.

Since Aug. 30, the Strickland campaign has spent about $2.6 million on paid media without any significant help from the Democratic Senatorial Campaign Committee or outside Democratic groups.

Portman and Republican groups have spent about $12 million since Aug. 30.

Reid Wilson contributed to this report.