But Democrats fighting to gain ground in Republican strongholds also collected staggering sums. In South Carolina, for instance, Democrat Jaime Harrison surpassed veteran Sen. Lindsey Graham, a close ally of the President, for the second fundraising quarter in a row.
The numbers illustrate that "Donald Trump is unifying and energizing Democratic donors all across the country," said Nathan Gonzales, editor of the nonpartisan "Inside Elections."
"Despite everything that's going on, we still have challengers breaking records, and small-dollar donations coming in, whether it's online, on the phone or through the mail," said Stewart Boss, a spokesman for the Democrats' Senate campaign arm.
The Democratic Senatorial Campaign Committee, meanwhile, raised $13.6 million in June, its best fundraising month of the election cycle -- bringing its second-quarter fundraising to nearly $34 million, Boss said.
Democrats need to net just four seats to flip control of the chamber; the number drops to three should Democrat Joe Biden win the presidency and his vice president becomes the tie-breaker in the Senate.
New reports filed Wednesday night with the Federal Election Commission show the Democrats' massive fundraising advantage in the Senate extends beyond the expected battlegrounds into states Trump won handily four years ago, including Kentucky, and even deep-red Mississippi.
A bright spot for Republicans came in Michigan, where the GOP challenger outraised first-term Democratic incumbent Sen. Gary Peters.
Here's a look at fundraising in some high-profile Senate contests:
In Arizona, Democrat Mark Kelly, a first-time candidate and retired astronaut, raised nearly $12.8 million, collecting about $3.5 million more than Republican Sen. Martha McSally.
Kelly -- who ran a gun-safety group with his wife, former congresswoman Gabrielle Giffords -- also has deep cash reserves to draw upon in the general election battle. He started July with nearly $24 million remaining in the bank to McSally's nearly $11 million.
McSally was appointed to John McCain's former seat in 2018.
John Hickenlooper, the former two-term Democratic governor, raised $5.2 million during the second quarter -- during which he had to fend off a primary challenge from former Colorado House speaker Andrew Romanoff.
Sen. Cory Gardner, the first-term Republican Hickenlooper hopes to oust, raised $3.6 million
Gardner had more than twice the available cash, almost $10.7 million to Hickenlooper's nearly $4.6 million.
The race is one of the most closely watched in the country because Colorado's politics have tilted left in the six years since Gardner narrowly won his Senate seat. The contest is rated a tossup by the nonpartisan Cook Political Report.
The state's Democratic Gov. Steve Bullock raised $7.8 million, outpacing the Republican incumbent he's trying to oust, Sen. Steve Daines, in another tossup contest.
Daines collected nearly $5 million during the April-to-June fundraising quarter. Both candidates had significant cash reserves: Bullock at nearly $7.6 million to Daines' $7.1 million
Businesswoman Theresa Greenfield raised $6 million in the second quarter, in what party officials said was a Democratic record for a Senate candidate from the Hawkeye State.
She outraised Republican Sen. Joni Ernst by about $2.4 million. Ernst, however, entered July with $9.1 million to spend in her campaign war chest to Greenfield's nearly $5.7 million.
In Maine, Sara Gideon, who survived a three-way Democratic primary this week, raised $9.4 million in the April-to-June fundraising quarter, besting Republican Sen. Susan Collins' $3.6 million haul.
Nationally, Democrats have made Collins a top target in their quest to flip control of the Senate.
Gideon, the speaker of Maine's House of Representatives, reported having $5.4 million remaining in the bank, just shy of Collins' $5.6 million war chest.
But Gideon's campaign also has access to nearly $4 million in crowd-sourced donations set aside by progressive groups for Collins' challenger that was raised as the senator weighed support and ultimately backed Brett Kavanaugh's ascension to the Supreme Court.
Democrat Cal Cunningham, an Army veteran challenging first-term Republican Sen. Thom Tillis, raised $7.4 million, nearly three times the amount Tillis raised in the three-month period.
Tillis' cash reserves were larger, however: $6.9 million to Cunningham's $6.6 million.
Both Georgia seats are up this year: Georgia GOP Sen. David Perdue is running for a second term and the other Republican incumbent, Sen. Kelly Loeffler, is seeking to fill the two remaining years of former Sen. Johnny Isakson's term.
Perdue raised $2.2 million, falling behind his Democratic challenger Jon Ossoff, who raised $3.9 million, including a $450,000 loan to his own campaign.
Perdue started July with a much deeper pool of cash reserves: $10.7 million. Ossoff had $2.5 million remaining in his war chest after winning last month's Democratic primary.
Loeffler's filings with the FEC show the wealthy businesswoman brought in $5.9 million for the special election -- and all but $912,000 came in the form of a loan from the candidate. Republican congressman Doug Collins raised $1.3 million.
Democrat Raphael Warnock, an Atlanta minister, raised $2.9 million.
The special election pits all candidates from all parties against each other on the same ballot in November.
McGrath, a former Marine fighter pilot, raised $17.4 million during the second quarter and had $16.2 million in available cash.
McConnell raised nearly $12.2 million and started July with nearly $16.7 million remaining in his war chest.
The Palmetto State is reliably red territory, but Harrison, the former South Carolina Democratic Party chairman, has raised eye-popping sums in his quest to topple Graham, the Senate Judiciary Committee chairman closely aligned with Trump.
Wednesday's night filings with the FEC show Harrison outraising Graham.
Harrison collected $14 million in the second quarter to Graham's $8.4 million.
Graham had more available cash remaining in his campaign accounts, $15 million. Harrison started July with nearly $10.2 million in reserves.
In Michigan, a perennial battleground state, the Republican challenger John James outraised Peters, the Democratic incumbent, by about $1.1 million during the second quarter.
Peters still entered July with a cash on hand advantage: He had $12 million available in his campaign account to James' $9.3 million.
The race for an open Senate seat in Kansas has drawn national attention and money -- much of it focused on shaping the Republican primary in which Kris Kobach, a fiercely conservative Republican, faces several challengers.
Kobach, an immigration hard-liner who ran unsuccessfully for Kansas governor in 2018, raised $233,000 in the April-to-June fundraising quarter and had just $145,000 in available cash.
US Rep. Roger Marshall, one of the other Republicans in the August 4 primary, raised $479,000 and started July with $1.1 million in available cash.
Democrat Barbara Bollier raised $3.7 million and started July with $4.4 million in remaining in the bank.
Trump won this state by nearly 18 percentage points four years ago. But the new filings show Democrat Mike Espy, a US Agriculture secretary in the Clinton administration, raised about $610,000 -- outpacing the Republican incumbent, Sen. Cindy Hyde-Smith, by 3-to-1.
Hyde-Smith still had far larger cash reserves: $1.2 million to Espy's $680,000.