Massachusetts Democrats have sent more than $34 million to senatorial campaigns across the United States in a growing effort to flip the Republican-led Senate, according to data released Monday by the nonprofit Center for Responsive Politics.

Local Democrats are giving heavily to candidates in states with close races — including Maine, Kentucky and South Carolina — making Massachusetts one of the top five donor states for two dozen Senate races across the nation, according to the new data.

Sara Gideon, Maine’s Democratic candidate for Senate, has collected the most from Massachusetts donors — more than $4.8 million — making Massachusetts the third-largest source of individual donations to her campaign, the center's data shows. Gideon, Maine's House speaker, is challenging Sen. Susan Collins, a four-term U.S. senator and the only remaining Republican member of Congress in New England. Collins has received about $520,000 from Massachusetts donors, making her the top Republican recipient of Massachusetts donations.

Massachusetts donors have also given $3.8 million to Jaime Harrison, who is challenging South Carolina Sen. Lindsey Graham, and about $3.5 million to Amy McGrath, who is running against Senate Majority Leader Mitch McConnell of Kentucky.

The center has tallied Federal Election Commission data over six years through Sept. 30 at its, but because of variations in filing deadlines, not all candidates’ donations are up to date. The location of the donor is only reported to the FEC if they contribute more than $200, so the Senate donation tallies do not include all of the small-dollar donations candidates have recieved, which could add up to millions.

Gus Bickford, chair of the Massachusetts Democratic Party, said earlier this year that the party launched a campaign called MobilizeMA to support national and local Democrats.

Bickford said Massachusetts Democrats are motivated to give by what they believe is a mishandling of the coronavirus pandemic, the country’s economic crisis, and President Donald Trump's nomination of Judge Amy Coney Barrett to the Supreme Court.

“Massachusetts Democrats have always played a big role in battleground states, and in 2020, we decided to take our program to an unprecedented level,’’ Bickford told GBH News in a prepared statement. “Folks are done with the GOP playing politics with their lives and livelihoods."

Democratic supporters have time and money to spare because Massachusetts Sen. Ed Markey is an overwhelming favoriteto win his race against Republican challenger Kevin O’Connor.

Siiri Morley of Jamaica Plain said the death of Supreme Court Justice Ruth Bader Ginsberg emphasized to her the importance of the Senate. She’s donated to a handful of senatorial campaigns outside of Massachusetts, she says, and has seen “a groundswell” of other people doing the same.

“It's clear that even if we change presidents in 2021, who is sitting in the Senate has a huge impact on what our president is able to do or not do,’’ she said.

Morley said she is particularly focused on Maine because she has family ties there.

It may not be surprising in a left-leaning state that the vast majority of Senate donations from Massachusetts are heading to Democrats. About 10% of donations from individual donors to out-of-state senatorial campaigns have gone to Republicans, data show. Massachusetts donors have sent about $500,000 to McConnell for his re-election campaign.

Massachusetts Democratic supporters are also donating their time to reaching out to voters across the country, writing letters, making phone calls and in some cases traveling to nearby states to knock on doors. Judith Herman of Concord has helped organize phone banks to contact North Carolina residents to convince them to vote blue.

Herman is a founding member of the Concord chapter of Indivisible, a national grassroots organization that focuses on electing progressive leaders to government.

“Because Massachusetts is a securely Democratic state,’’ she said, “we can channel our time, funds and energy to focus on a really pivotal state in this critical election.”

Isabel Contreras is an intern with the GBH News Center for Investigative Reporting.