Thirteen liberal groups told Senate Minority Leader Chuck Schumer Wednesday that he is failing to fight hard enough to keep Brett Kavanaugh off the Supreme Court.

"The Supreme Court is on the line, and you are failing us," they wrote in a letter Wednesday morning.

Democratic senators sought to delay the hearing Tuesday, and interrupted Republicans dozens of times during the first day of Kavanaugh's confirmation hearing. But even though Democrats are powerless to stop him, the liberal groups said they need to try harder — mostly by making clear their opposition to the nominee.

"Your job as Senate Democratic leader is to lead your caucus in complete opposition to Trump's attempted Supreme Court takeover and to defend everyone threatened by a Trump Supreme Court," the groups wrote. "But unbelievably, nearly two dozen Democrats have still not come out against Kavanaugh, and just last week, you helped Majority Leader Mitch McConnell fast track 15 Trump judicial nominees."

"That is not the leadership we need," they warned.

The groups said that only by keeping all 49 Democrats together do they have a chance to turn a few Republicans against Kavanaugh. They said Schumer's strategy seems more aimed at not losing any Democratic seats rather than stop Kavanaugh.

"Your strategy to sacrifice the Supreme Court in order to hold Democratic Senate seats is not only strategically and morally wrong, it will fail," they wrote. "It is wrong to assume that a no vote on Kavanaugh puts red-state Democrats in electoral peril or somehow protects them from Republican attacks."

It concluded by saying failure to hold all 49 Democrats against Kavanaugh would be a "massive failure of your leadership." The letter was signed by CREDO, Democracy for America, Friends of the Earth, Demand Progress and others.

The letter is the latest sign that congressional Democrats are under pressure from liberal and progressive groups to take on more extreme positions. Several new Democratic candidates have said they would not support House Minority Leader Nancy Pelosi if Democrats take over the House.

[Opinion: Democrats have a point on Brett Kavanaugh documents, but GOP should stick to confirmation timeline]