Like Obama, Truman had suffered a resounding defeat in the 1946 Congressional elections. In fact, it was even worse for him; he lost control of both the House and the Senate. And like Obama, he confronted an emboldened Republican Congress that refused to pass his program (and unlike Obama, he had several of his vetoes overridden). And when he ran for re-election, here's what he didn't do: talk about amity and compromise and cooperation. The other side wasn't interested, and Truman knew it. So what he did was draw clear lines and make a principled fight.
This version is Hollywood, not history. As Brendan Nyhan noted last November, Truman won because of a good economy, not a good acceptance speech. Moreover, Dewey was a fine governor who might have made a first-rate president, but in 1948 he was a weak candidate who ran a bland campaign. The 2012 GOP candidate will probably be a tougher foe than Dewey was.