“The key for me was to focus on the tight races outside of Massachusetts,” he said. “That was a strategic decision.”

Guernsey’s calculation is one shared by other deep-pocketed donors in wealthy Massachusetts, which this year, as in most past cycles, has few competitive races of its own. A Globe analysis of the top 500 contributions from Massachusetts residents in 2024 showed a steady stream of money toward mostly Democratic and nonpartisan super PACs across the country, but also a number of such Republican political groups benefiting from the largesse of Massachusetts donors.

The trend is one analysts say springs both from the deep political division in the US and the lingering effects of a 2010 Supreme Court decision that allows for unlimited donations to super PACs, which are also allowed to spend unlimited amounts of money on political activity but cannot, for the most part, coordinate with candidates.

“You have two parties that are polarized and they are on the knife’s edge of who is going to control government,” said Ray La Raja, a professor of political science at the University of Massachusetts Amherst. “That is a recipe for pouring money into contests.”

The dynamic is especially true in Massachusetts, La Raja said, where politicians from all over the country swing through to raise money from the state’s well-heeled donor class. High-dollar fund-raisers attract Democrat and Republican candidates from elsewhere up and down the ticket, and serial donors work closely with the parties to direct their donations, La Raja said.

This cycle, Republican vice presidential candidate JD Vance attended a luncheon in Gloucester, Vice President Kamala Harris raised money in Pittsfield and Provincetown. In tony Martha’s Vineyard, buzzy names in Democratic politics, from Maryland Governor Wes Moore to New York Attorney General Letitia James, have spent the summer taking turns tapping into the donor base.

Massachusetts has among the highest median household incomes in the US and is home to some of the wealthiest people in the country. And according to campaign finance data compiled by watchdog group Open Secrets, it ranked ninth in political giving this cycle despite being the sixteenth-most populous state.

“Major donors who give repeatedly are partisans. They are true believers. They want the policies of their parties implemented,” La Raja said. “So they are willing to send money to Wisconsin so their party controls Congress.”

Because there are few competitive states, donors in the wealthiest pockets of the country tend to funnel large amounts of money to the few dozen tight congressional races or to the presidential election.

While Democrats dominate Massachusetts politics, political giving by wealthy Massachusetts benefactors spans the political spectrum.

Republican donors, including New Balance chief Jim Davis, have poured money into causes working to support Republican women, elect Donald Trump to a second term or, alternately, back a conservative-run group opposed to Trump’s reelection. Many in Massachusetts funded a committee backing former US ambassador to the United Nations Nikki Haley to be the Republican party’s presidential nominee.

The Republican donors whom the Globe contacted for comment declined to do so or did not respond.

Democratic donors such as Cambridge music scholar and donor Jay Scheide and Suffolk Construction CEO John Fish have funneled millions into committees working to elevate Vice President Kamala Harris to the White House, elect pro-choice Democrats into office, and support Democrats in swing states.

Members of both parties have poured tens of millions into a super PAC promoting pro-Israel candidates, while others sent large donations to a cause working to get voters to blank their ballots in protest of the Israel–Hamas war as part of the national “uncommitted movement.”

“Money has just become more and more important. I think it’s a phenomenon across the donor universe,” said Maurice Cunningham, a University of Massachusetts Boston professor who regularly writes about state campaign finance law. “I see a lot of billionaire donors casting their influence in different states.”

In Western Massachusetts, Guernsey’s team sent 600,000 postcards supporting Democrats in states such as Pennsylvania, New York, and Ohio, and put up billboards and digital ads supporting President Biden before he ended his campaign.

As an individual, Guernsey has given nearly $1 million of his own money to similar Democratic causes this year.

“The most important need this year is to protect our country. The only way we can do that is protecting outside, where there is much more risk of losing to a demagogue,” Guernsey said of Trump. “There is a total understanding of the donors here in Massachusetts that unless you have a local race that demands your attention … most people are making large donations outside the state.”

The flow of money out of state is a relatively new phenomenon, said Ian Vandewalker, senior counsel and manager for the Brennan Center’s Elections and Government Program.

In 1998, candidates for the US House overall raised more than 80 percent of their campaign money from their home states; in 2022, that percentage was down to just over 60 percent, according to research conducted by the Brennan Center.

The concept of sending money out of state goes beyond mega-donors, too. According to a recent UMass Amherst/WCVB poll, 49 percent of 700 likely voters in the state have either attended a rally, sent money to out-of-state candidates or groups, or posted to social media about an election in a more electorally competitive state.

Vandewalker said that the polarization of today’s Congress has led to a scenario where control can change nearly every election cycle, meaning a person’s vote is no longer enough to help one party gain control in Washington. Sending money to districts with competitive races, however, can.

“It used to be the case that candidates for Congress raised most of their money from residents of their district,” Vandewalker said. “Now that has flipped.”

Samantha J. Gross can be reached at samantha.gross@globe.com. Follow her @samanthajgross.