WASHINGTON—Top Senate Democrats called on President Trump to immediately declassify the White House notification to Congress of the drone strike last week that killed prominent Iranian military leader Qassem Soleimani.

“It is critical that national security matters of such import be shared with the American people in a timely manner,” wrote Senate Minority Leader Chuck Schumer and Sen. Robert Menendez, the top Democrat on the Foreign Relations Committee, in a letter Monday.

...