Truman is now seen as a near-great president because he put in place the containment doctrine boosted by the Truman Doctrine and the Marshall Plan and NATO, which historians now see as having been at the center of American success in the cold war.
When President Obama first unveiled his gun control proposals recommending a ban on assault weapons and high-capacity magazines and better background checks, there seemed to be momentum behind the effort. But then the proposals ran into a wall.
Vice President Biden's surprising declaration of unqualified support for gay marriage seems to have forced President Obama into a public endorsement of a controversial social issue. It is difficult not to suspect that Biden's pronouncement aimed to give the president some political cover.
If nobody trusts you as president, then you can't get anything done.
The consequence of the Bay of Pigs failure wasn't an acceptance of Castro and his control of Cuba but, rather, a renewed determination to bring him down by stealth.
As someone who has more than a passing acquaintance with most of the 20th century presidents, I have often thought that their accomplishments have little staying power in shaping popular views of their leadership.