I don't know if this is true at all. I don't think Truman, Ford, or Bush 41 ever served in the U.S. Senate. And even if they all did, you'd also have to consider that McGovern, Mondale, Dole, Gore, and Kerry -- arguably the five worst candidates for an executive office in the history of mankind -- were all former U.S. Senators.
The rest is pure coincidence.
No, it's not. Most U.S. Senators are unmotivated, lazy, chummy people by nature who are more interested in getting along with the other members of their exclusive club than in getting things done and taking principled stands. Most governors, on the other hand, are leaders by nature because they serve in an executive capacity.
Jon Corzine was a high-powered executive at Goldman Sachs who spent $68 million of his own money to run for the U.S. Senate in New Jersey in 2000. He was bored out of his mind within six months, and set his sights on running for governor of New Jersey sometime after that. In what was probably the worst return on a $68 million investment in the history of politics, he'll probably win in November and won't even finish his one term in office in Washington.
"I don't know if this is true at all. I don't think Truman, Ford, or Bush 41 ever served in the U.S. Senate."
Yes, they were all senators.
"And even if they all did, you'd also have to consider that McGovern, Mondale, Dole, Gore, and Kerry"
So what? Some won, some lost. That's not a curse, that's a normal distribution.
Truman served in the senate but the others did not. Ford and Bush 41 were both Representatives in the House at one time though.