Democratic Senate candidates from Arizona to South Carolina raised tens of millions of dollars in the second quarter for campaigns to unseat Republican senators, adding more resources to their fight to retake the Senate majority in November.

Jaime Harrison, the Democrat challenging GOP Sen. Lindsey Graham in November, reported raising nearly $14 million in the last three months, nearly doubling his fundraising total at the start of the year. Graham has not yet reported his fundraising totals for the quarter.

Amy McGrath, the newly-minted Democratic nominee who is seeking to topple Senate Majority Leader Mitch McConnell, raked in an astonishing $17.4 million to mount her uphill climb in deep red Kentucky, according to a campaign spokesperson. That amount is more than two times McConnell's fundraising total from the first quarter of 2020, when he raised $7.5 million. McConnell has yet to release his latest fundraising numbers ahead of the July 15 deadline.

In Maine, Sara Gideon, the Democratic speaker of the statehouse, challenging longtime Sen. Susan Collins, said last week that she raised $9 million for her campaign this quarter, roughly triple the amount Collins raised, according to preliminary filings from the GOP senator's campaign.

Collins is up against the toughest matchup of her career, and while her challenger isn't set just yet, Gideon is favored to win the primary next Tuesday.

From the onset of the cycle, Republicans faced a tougher map, with the party defending 23 seats, compared to Democrats' 12 seats. Nearly a dozen seats are competitive between the two sides, but with Republicans holding 53 seats in the Senate, Democrats need to flip four seats to retake the chamber -- or three if former Vice President Joe Biden defeats President Donald Trump.

With the president's standing slipping in many states as the coronavirus continues to spread across the United States, and the country grapples with renewed debate over systemic racism, Democrats have been buoyed across the Senate map.

Candidates like Harrison, who is seen as a long-shot against Graham in deep red South Carolina, have raised prolific sums of money to spend aggressively in races that were not expected to be in play this cycle.

Last year, Democrats' path to at least a 50-50 split, according to Dr. Larry Sabato, the director of the University of Virginia's Center for Politics, was a "possibility" but not necessarily the "probability."

"Now, I still wouldn't call it the probability, but I would say, at worst, for Democrats is 50-50 — and I don't mean 50-50 Senate seats — I mean that it's a coin flip as to which party will control the Senate," he said. "That's a surprise, because Democrats originally didn't have that many targets. But, a lot has happened, and most of it has played into Democratic hands."

In some of the most competitive contests across the battlefield, and in some states Trump carried in 2016, Democrats are bringing in stockpiles of cash reminiscent of the fundraising of some House Democratic candidates who helped the party flip the chamber in the 2018 midterms. The fundraising could complicate Republicans' efforts to limit the number of seats actively in play in November.

"Democrats are just determined to first get Trump out, but second, to make Republicans in the Senate pay a big price for what they have done, which is basically losing the entire purpose of the Senate," Sabato told ABC News.

In Montana, which Trump carried by 20 points, Gov. Steve Bullock brought in a massive $7.7 million haul after he entered the race against freshman GOP Sen. Steve Daines in March. His total, the first full quarter for his Senate campaign, is more than the three times the amount he raised in the last quarter of his short-lived White House run.

Daines has not released his fundraising totals yet for the reporting period, but in the first quarter of this year, he raised only $1.3 million. Bullock's full pockets show just how high of a priority the race has turned for Democrats since his entry.

In North Carolina, the site of one of this cycle's most competitive Senate matchups, Cal Cunningham, a former Democratic state senator and Army veteran, raised $7.4 million over the three-month period that stretches from April to June, in his bid to unseat GOP Sen. Thom Tillis.

Tillis has not yet released his fundraising totals for the quarter, but during the first three months of the year, he brought in $2.1 million, falling short of Cunningham's $4.4 million. Still, Tillis holds onto a $3.5 million cash-on-hand advantage.

But Tillis is in need of a boon, after a recent poll from the New York Times/Siena College showed Cunningham leading, 42%-39%, among registered voters in the Tar Heel state.

In Georgia, Jon Ossoff, the Democratic nominee and former congressional candidate, raised $3.5 million, which could bring him closer to leveling the financial playing field against Republican incumbent Sen. David Perdue. Despite raising only $1.7 million in the first quarter, Perdue ended the reporting period with $9 million on hand -- far outpacing Ossoff's $1.8 million in the bank.

Republicans, despite the large sums from their Democratic challengers, are brushing off concerns about a fundraising deficit.

"Democrats will need to spend every penny to defend records that are disqualifying in the eyes of mainstream voters who will decide the outcome in key Senate races," said Jesse Hunt, a spokesperson for Senate Republicans' campaign arm. "Personal scandals and a party rallying around a socialist agenda are problems money can't solve."

Republican operative Brian Reisinger told ABC News that Democrats' fundraising -- along with Trump's current unpopularity in many states -- shouldn't change how Republicans defend their seats.

"A good Senate race… ought to be run like a sheriff's race, really down to the roots local. That's the way that it should always be done, whether the national ticket is helpful or harmful," he said.

Reisinger led communications for Sen. Ron Johnson's 2016 reelection campaign, when the senator was written off by many GOP groups, and widely expected to lose along with Trump.

Instead, Johnson defied expectations and won reelection handily, while Trump won Wisconsin, making it the first time the state went for Republicans on the presidential level since 1984.

"It's way too early to say whether there is truly a weight around the necks of Republicans," he said. "It's very fashionable to say it's a bad environment for them, but we're four months away. A lot of things can change."

Some numbers from some of this cycle's most closely-watched races, though, are still outstanding.

In Iowa, another state where the president is popular, Sen. Joni Ernst is fending off Democrat Theresa Greenfield. Fundraising totals from both candidates are still to come, but Greenfield narrowly outraised Ernst between April 1 to May 13, leaving Ernst with an edge in the bank of just over $2 million. In their pre-primary filings from May, Greenfield raised $1.5 million, compared to Ernst's $1.2 million.

But in the first quarter of the year, Greenfield trialed Ernst in fundraising, with $2.25 million compared to the incumbent's $2.74 million.

Greenfield's campaign said on Twitter that they raised $200,000 in two days online after Ernst appeared as a guest on CNN and seemingly defended Trump's handling of the coronavirus pandemic.

And in Arizona -- a state where Democrats see one of their best chances of ousting an incumbent Republican -- Mark Kelly, a Democrat and former U.S. Navy captain, has far outpaced his rival, Sen. Martha McSally.

In first quarter filings, Kelly raised $11 million, nearly double McSally's $6.4 million. The race is expected to be among the most competitive, with Kelly leading McSally, 47%-38%, in the New York Times/Siena College poll

The shifting electoral fortunes for the GOP comes as dual crises roil the 2020 election, with Republicans balancing their loyalty to Trump against both the public's broad disapproval of his handling of the coronavirus pandemic, and the president's brash response to the nationwide unrest over racial injustice and penchant to inflame racial tensions.

Trump is currently confronting declining support in recent national and battleground polling, which could imperil vulnerable Senate incumbents and ultimately threaten the party's majority.

The current circumstances for Trump, Sabato said, are similar to the 1980 presidential election, when Republicans gained a net of 12 seats and the majority for the first time since the early 1950s.

"1980 clearly was a terrible year for Democrats, and it was obvious as we built up to the election that everything was going wrong for them: economic policy, foreign policy, the party split between [Ted] Kennedy and [Jimmy] Carter," he said. "Everything was coming together nicely, not just for [Ronald] Reagan, but for the Republicans down ticket."

"There's some similarity to that, though we're four months out... who knows what's gonna happen," he added.