President Joe Biden was not sold on sending Abrams tanks to Ukraine. Neither were military leaders. But Secretary of State Antony Blinken had a pitch, and Biden began to warm to an idea that might satisfy the Pentagon and mend public divisions in the U.S.-European alliance over sending the tanks, three U.S. officials said.

The president’s ultimate reversal caught some military officials by surprise, three people familiar with the matter said. The decision exposed a tension between wanting to give Ukraine what it’s asking for and what makes sense on the battlefield, a gap that is likely to grow as the war drags on, the officials said.