RECENT NEWS REPORTS have suggested that US Rep. Joe Kennedy III is seriously considering challenging Sen. Ed Markey in the Democratic primary. We are writing to say, in no uncertain terms, and in no disrespect to the congressman, that this is the wrong time for an intra-party challenge.

First off, it has been clear that Markey has been a pivotal leader when it comes to climate change, and arguably has one of the most important roles to play in a very narrow window of time to advance climate action. The next six years will likely determine whether and how our nation rises to the occasion on climate change. Do we mobilize fully to address this challenge head-on through policies like the Green New Deal that Markey and Rep. Alexandria Ocasio-Cortez filed? Or do we continue on a path of death-by-gradualism, where we fail to provide a bold and comprehensive solution to climate change?

To his credit, Kennedy joined with 7 of his fellow 8 Massachusetts representatives and Sen. Elizabeth Warren as a co-sponsor of the Markey-Ocasio-Cortez Green New Deal resolution. It’s the best shot we have to advance climate action in our nation, and one that Kennedy would be wise not to disturb if he truly shares our goals of a livable climate for all.

The beautiful part of this Green New Deal partnership is that it paired the bold vision of a first-term congresswoman (Ocasio-Cortez) with the institutional knowledge of an established climate leader (Markey). Together, they were able to combine a fresh, bold vision with policy know-how.

It’s true that Markey has been in Congress for a long time, but that’s exactly why we need him to see his climate change work through to completion. Markey previously chaired the House Select Committee on Climate Change, and helped shepherd the Waxman-Markey bill through the House. We need someone with his institutional knowledge and standing to help shepherd the Green New Deal through the next Congress.

The role of young visionary leader in this partnership is already occupied by Ocasio-Cortez. If  Kennedy were to replace Markey in his current Senate seat, who would be present to partner their institutional knowledge and subject matter expertise (to say nothing of passion) with Ocasio-Cortez’s visionary call for change? That’s not a role that a theoretical Sen. Kennedy, or any other sitting senator, could easily pick up. And that role will be one of the most important roles any political leader will play in the next six years.

That’s why Markey can count on such strong backing from progressives, youth, and climate hawks; he will not be easy to take down. But think of the message it would send nationally if Kennedy succeeded in his primary challenge. Fox News would have a field day, spreading the narrative that the Green New Deal can’t even be defended in Massachusetts primary elections, to say nothing of general elections in purple and red states. That would basically be the death knell for the Green New Deal.

Quite simply, we need Markey where he is, and we need Kennedy where he is, too. Rather than forcing Democrats to spend $10-plus million on a costly intra-party battle, Kennedy could show real leadership by dedicating his resources to helping re-elect Markey and help win important House and Senate battles in other states so that we enter 2021 with as much Democratic support as possible to help pass bold, sweeping, and equitable climate legislation.

We were proud to support then-City Councilor Ayanna Pressley in her bid to challenge US Rep. Michael Capuano for reasons of vision, life experience, and representation. With all due respect to Kennedy, he would not add much to the lived experience present in the US Senate or helping represent under-represented voices currently left out of policy debates. (Indeed, while Pressley was set to be the first woman of color to represent Massachusetts in Congress, Kennedy would be the umpteenth white man and third member of his extended family to represent Massachusetts in the US Senate.)

We need Kennedy to continue to bring his political savvy, fundraising prowess, charisma, and vision to the fight for our nation’s soul in the US House of Representatives, and we need Markey to continue to bring his passion, policy know-how, and vision for an equitable and rapid path to address climate change in the US Senate.

Craig S. Altemose is executive director of 350 Mass Action, Deb Pasternak is director of the Massachusetts chapter of the Sierra Club, and Varshini Prakash is executive director of the Sunrise Movement.