Truman listens to certain people who tell him he should get tough with the Russians. At his first meeting with Molotov, the Soviet Foreign Minister said “I have never been talked to like that in my life.”
“Carry out your agreements and you won’t get talked to like that,” Truman replied.
Then Truman decides to look tough by ending the Lend Lease shipments to the Soviets. Unfortunately nobody seems to have told him that the USA was still counting on Soviet support to end the Pacific War.