Joe Kennedy doesn’t have to just beat incumbent Ed Markey to win a Senate seat. He’ll also have to trounce Chuck Schumer, Elizabeth Warren, Senate Democrats’ campaign arm — and maybe Alexandria Ocasio-Cortez.

The 38-year-old congressman and grandson of Robert F. Kennedy will confront a buzz saw of Washington Democrats if he takes the leap to challenge the Massachusetts senator, a move that would create a massive distraction for the party in a safe Democratic state amid a battle for both the White House and the Senate majority.

“That kind of intraparty fighting is not good in the long term. And I don’t think it will be good for Joe Kennedy,” Sen. Jeanne Shaheen (D-N.H.) warned. “I’m a survivor of the [Ted] Kennedy-[Jimmy] Carter fight. I know how long those sentiments last.”

With Kennedy flirting with the race and leading in early polls, Markey has moved quickly to shore up support from both the Washington establishment and prominent progressives. Rep. Ro Khanna (D-Calif.) has endorsed him, and Schumer said the party is “fully behind Sen. Ed Markey.” Kennedy called Schumer about the race, but the Senate minority leader didn’t divulge what was said.

Markey also asked Ocasio-Cortez for her support, according to a source familiar with the matter. The liberal firebrand said endorsing Markey is “in the realm of possibility.”

Kennedy isn’t without allies. Sen. Kyrsten Sinema of Arizona, a moderate Democrat who served with Kennedy in the House, is urging him to run and told Markey of her decision on the Senate floor Wednesday afternoon.

“Joe Kennedy is an outstanding champion for his state,” Sinema said. “He’s a fresh thinker who can bring people together to get things done. He will make a terrific U.S. senator, and I couldn’t be more proud to support my friend.”

But the support of Schumer and moderate Sen. Joe Manchin (D-W.Va.) for Markey, along with the incumbent’s close relationship with Ocasio-Cortez as original co-sponsors of the ”Green New Deal,” demonstrates that the potential Senate race won’t revolve around ideological conflicts like the GOP’s tea party wave of a decade ago.

Instead, the contest is shaping up to be generational: The youthful Kennedy and his famous family brand against Markey’s 40-plus years of service and lengthy liberal record.

“I don’t understand how anyone wants to run against him — I mean he is the progressive leader on climate in the United States Congress,” Khanna, a leading liberal lawmaker, said of Markey. “The progressive base is 100 percent for Markey — it’s 110 percent for Markey.”

“I would tell Joe to wait,” Manchin, the Senate’s most conservative Democrat, said. “Those type of fights when two people are aligned ideologically? What’s the fight?”

The Massachusetts delegation is behind Markey, save for three members who have yet to weigh in, including progressive star Ayanna Pressley, who upset longtime Rep. Mike Capuano in a primary last fall. Kennedy’s challenge to the old guard has perplexed senators, who see him as trying to climb the political ladder at the expense of his state’s seniority.

But many of his House colleagues are quietly rooting for him, eager to demonstrate one of their own can advance without waiting until senators retire or their longtime leaders depart the top rungs of the House Democratic Caucus.

And Markey’s supporters in the Senate aren’t trashing Kennedy. After all, he could be a future colleague or presidential candidate given his lineage and reputation as an ascendant voice in the party.

“Ed has been a great partner in the Senate, and I was glad to endorse him last February. Joe is doing a terrific job in Congress. They both are longtime friends,” Warren said in an interview. Warren was Kennedy’s professor at Harvard University.

In an interview on Wednesday, Markey touted his endorsement from NARAL Pro-Choice America, the League of Conservation Voters, senators and state lawmakers. Asked about polls showing Kennedy with an edge, he replied: “I’m getting tremendous support.”

“So far the response I’m getting is overwhelmingly positive,” he said. “I’ve led on climate change, led on gun reform, led on reproductive rights and protections for women … people are grateful.”

Markey said he hasn’t spoken to Kennedy recently.

Kennedy is expected to make a decision by the end of the month, according to a campaign aide. Kennedy spokeswoman Emily Kaufman said the congressman is still deliberating but is “encouraged” by his support.

“If he decides to run, it will be based on the people of Massachusetts — and them alone,” Kaufman said.

Despite Kennedy’s famous last name, he’s kept a low profile since arriving in the House in 2013. He has resisted calls to join House leadership, focusing instead on elevating younger members of a caucus run by septuagenarian leaders. He did deliver the State of the Union response last year, a job usually reserved for the party’s rising stars, although his speech is mostly remembered for the prominent smudge of lip balm that some viewers mistook for drool.

After nearly 40 years in the House, Markey won a special election to replace John Kerry in 2013 and is a leading liberal lawmaker in the Senate, though not necessarily a partisan firebrand. He has one of the thickest accents in Congress, sometimes referred to as Ed “Mahkey.” He voted “present” on war with Syria shortly after being sworn in, annoying “literally everyone,” as Boston magazine put it.

Several House Democrats were reluctant to weigh in on the potential primary. Some said privately they’re convinced Kennedy is running. And they offered effusive praise for the four-term lawmaker, who has developed a cadre of friends on both sides of the aisle.

“Joe Kennedy might be the most popular member of the Class of 2012 in both parties,” Rep. Scott Peters (D-Calif.) said. “Massachusetts and the country will find a good place for Joe Kennedy to serve. It may not be in House leadership, but he has a great future.”

As the heir to a dynasty, Kennedy appears an instant front-runner in any statewide race. There’s private skepticism among some Democrats that the Democratic Senatorial Campaign Committee will spend money in a primary in a state seen as uncompetitive in a general election, though DSCC Chairwoman Catherine Cortez Masto said the party is behind Markey. The primary would be in September 2020 — poor timing for party unity.

Kennedy has a double-digit lead in early polls in a potential race against Markey. And he could potentially scare Markey into retirement or position himself for the next Senate vacancy if Warren becomes president.

But Markey isn’t surrendering, and there’s really no room to his left for Kennedy to pursue. He’s telling fellow senators that he is not retiring and will run hard against Kennedy, according to those who have spoken with him.

“It’s ambition,” Senate Minority Whip Dick Durbin said of Kennedy’s motivation. “For Ed’s sake, I don’t want a primary. … He’s clearly running for reelection. And I’m going to help him in any way I can.”

The show of support from top Democratic leaders and progressives suggests there’s some worry that Markey could lose to Kennedy or at a minimum drain money from the party’s coffers. So if Kennedy runs, Democrats are preparing for a wild ride.

“That’s life in a blue state,” said Sen. Jon Tester (D-Mont.), a former DSCC chairman. “The Kennedy name probably has a little bit of stroke in Massachusetts. So chances are it might be” competitive.

Melanie Zanona contributed to this report.