As Democrats scramble to retain their narrow House majority and gain control of the Senate in 2020, a potential primary between Senator Ed Markey and Representative Joseph P. Kennedy III could divert tens of millions of dollars in campaign contributions away from competitive congressional races against Republicans around the country.

A high-stakes Massachusetts primary also would make it highly unlikely that Markey and Kennedy could funnel as much of their own campaign cash to other candidates as they have in the past and hinder the ability of Kennedy, a sought-after speaker because of his legendary lastname, to headline Democratic fund-raising events around the country.

Analysts said the loss of money wouldn’t be a major blow to Democrats’ 2020 efforts, but certainly wouldn’t help in what is expected to be a difficult battle with Republicans for control of Congress.

“The most frustrating thing about any primary is that it sucks resources from candidates in competitive races elsewhere,’’ said Steve Israel, former chairman of the Democratic Congressional Campaign Committee, which works to elect Democrats to the House.

A primary forces incumbents who are in safely Democratic or Republican seats to horde their money instead of giving it to candidates in more competitive races, Israel said.

“Bottom line, every dollar that’s spent on a primary in a blue or a red state is a dollar less for candidates who need it in purple states,’’ he said.

Kennedy, 38, a four-term congressman and the grandson of the late senator Robert F. Kennedy, has said he is considering a primary challenge against Markey, 73, who has served in the Senate since 2013 after 37 years in the House.

Kennedy would hold an immediate edge over Markey if he decided to run, according to a new Suffolk University/Boston Globe poll published Sunday.

Kennedy would lead a five-person field by 9 percentage points, 35 percent to Markey’s 26 percent, according to the survey of likely 2020 Democratic primary voters conducted by the Suffolk University Political Research Center.

And in a head-to-head matchup, Kennedy’s advantage would grow even larger: 14 percentage points — 42 percent to 28 percent, the poll stated. He would best Markey in every age group and across wide geographic swaths of the state.

Such a race would be the highest-profile congressional primary in the country next year, pitting the scion of one of America’s most famous political families against a well-liked, liberal senator who shares most of the same political views. Some Democrats have griped that the party needs to be working together to defeat President Trump and the Republicans rather than engaging in an expensive intraparty fight.

And any time Kennedy spends knocking on doors in Massachusetts means less time at fund-raisers to help other Democrats.

In 2017, Kennedy was the keynote speaker at the annual fund-raiser for the Texas Democratic Party. He also attended a fund-raiser that year for Chicago Democratic Representative Cheri Bustos, who now serves as chairwoman for the DCCC. And last year, his efforts included headlining fund-raising dinners held by local Democratic parties in Carroll County in New Hampshire and Broward County in Florida.

In the 2018 midterm elections, Kennedy pumped $5 million into Democratic campaigns across the country by donating to them directly or indirectly through party organizations as well as appearing at fund-raisers on their behalf, according to his campaign.

So far this year, he already has raised $1.7 million for others.

A campaign spokeswoman said last week Kennedy would continue to help other candidates even if he runs, but did not specifically say he would continue to appear at as many fund-raisers.

“Congressman Kennedy will always work hard to support Democratic candidates in Massachusetts and across the country, no matter the race he is running,’’ said spokeswoman Emily Kaufman.

Between the 2018 and 2020 cycle, Markey contributed and raised approximately $2 million for Democratic congressional candidates, a Markey spokeswoman said.

Markey and Kennedy have about $4 million each in their personal campaign accounts, according to the Center for Responsive Politics, a nonpartisan research group that tracks election spending. Each candidate also has a political action committee, which they use to funnel money directly to other candidates.

In the 2018 midterms, for example, Kennedy’s PAC, 4MA, contributed $304,000 to other House and Senate candidates. Most was given to competitive races, including those of Katie Porter in California, who defeated a Republican incumbent, and Kyrsten Sinema in Arizona, who won a tight race to fill the seat of a retiring Republican.

Markey’s PAC, Educate & Innovate, gave $113,500 to other federal candidates in the 2018 cycle, also focusing on competitive races such as those of Senators Bob Casey of Pennsylvania, Jon Tester of Montana, and Claire McCaskill of Missouri.

But while a Massachusetts primary would likely siphon money away from other Democratic races, it might not hurt the party’s cause that much, some analysts said. In the Trump era, Democratic donors are proving more generous than ever and appear willing to give whatever it takes to win back more power in Washington.

“I think the last thing Democrats are going to have to worry about this cycle is money,’’ said Jim Manley, a Democratic political strategist who worked as an aide to the late Massachusetts Senator Edward M. Kennedy. “As far as I can tell, everyone involved across the country is going to have more than enough money to run competitive races.’’

It is unclear how much this race might cost, but it could be a lot. As a potential gauge, Jennifer Duffy, a senior editor of the Cook Political Report, pointed to the competitive Massachusetts Senate race in 2012 between Elizabeth Warren and Republican Scott Brown, which cost a combined $77 million, according to the Center for Responsive Politics.

A Kennedy-Markey race could have other ripple effects on fund-raising. It could suck money away from other state primaries, like the one between Representative Richard Neal of Springfield and Alex Morse, the 30-year-old mayor of Holyoke who plans to challenge him.

Morse is running as a more progressive candidate than Neal, 70, who has been in Congress since 1988. He serves in a powerful post as chairman of the House Ways and Means Committee.

Laura Krantz can be reached at laura.krantz@globe.com. Follow her on Twitter @laurakrantz.