He was a member of the Pendergast gang in Missouri. He took a proactive role in stealing the Senate seat from Coke Stephensen and giving it to LBJ. He didn't do what was right he did what was evil.
He presided over an administration that was chock full of commies and he knew it. He did everything he could to support them and attacked the ones trying to rid the government of them.
It was necessary for Truman, Johnson, and their ilk of big-spending socialists to make certain that Speaker Coke didn't interfere with their grand social programs.
Besides stuffing Ballot Box #13, Truman and Johnson used Yale attorney Abe Fortas to seal their LBJ Senate election theft (a favor repaid by nominating Fortas to the Supreme Court later - which further begets the whole Chief Justice Warren Harding/President Nixon feud, et al, including Fortas' eventual resignation from the Supreme Court - the first to ever do so - after getting caught accepting a $20,000 bribe masked as a retirement pension payment).