Sen. Joe Manchin (D-W.Va.) warned the U.S. must move to support Ukraine in the war against Russia, or face the "worst atrocity in history" at Axios' annual What's Next Summit in Washington, DC.

Why it matters: Congress has been deadlocked over further aid to Ukraine as the White House and foreign leaders warn the support is direly needed.

• The Senate passed a $95 billion Ukraine aid package in February, but conservative backlash in the House has left the measure dormant.
• President Biden has repeatedly pleaded for lawmakers to send him a funding package for Ukraine, including during his most recent State of the Union.

The big picture: Senate Minority Leader Mitch McConnell (R-Ky.) has repeatedly pressured House Speaker Mike Johnson (R-La.) to bring the Ukraine aid to a vote.

• But the speaker has so far refused, and lawmakers have been busy trying to avoid a domestic government shutdown for weeks.

What they're saying: Manchin said "God help us" if the U.S. does not pass Ukraine support before the end of spring.

• "That'll be the worst atrocity in history that your children or grandchildren will be reading about," Manchin told Axios' Niala Boodhoo.

Zoom out: Manchin's comments on Ukraine come as he nears the end of his final Senate term. His decision to retire all but cedes his West Virginia Senate seat to Republicans, with Democrats facing an uphill battle to keep control of the chamber in November.

• Manchin has criticized Biden for being pushed too far to left, arguing it will doom his re-election bid.

Go deeper: Centrist extinction looms as Sinema, Manchin, Romney call it quits