The best time to lose an election is just before the country tips into recession. Then your opponent can take the blame, and if you play your cards right you should be able to win the following two elections at least. That doesn't mean that any politician ever wants to lose an election, but there may sometimes be elections that they don't fight quite as hard.
After the Australian elections last year, Ross Gittins suggested that the Labour win was a poisoned chalice, because the Labour Prime Minister was likely to preside over economic decline.
So how much does the Republican Party really want to win the US election this year? It's not as if Senator McCain was overwhelmingly popular with the party establishment. Governor Palin is incredibly popular with some sectors of the population, and treated as a joke by most other sectors. Surely if they really wanted to win, they'd have picked someone else. Therefore perhaps they don't really want to win. Let President Obama screw up for four years and then the Republicans can have the White House back plus a strong majority in both houses, plus a popular mandate to undo any reforms that President Obama might have forced through.
According to the fears and hopes of the Republican party, Obama's presidency may be like Carter's, bad while it lasts but paving the way for another great Republican president. Parts of the Democratic Party hope and believe they are wrong, while perhaps other parts think that Carter was just ahead of his time.