Quite a few mainstream economists say it's a bad idea. And the decision reeks of desperation politics. From the NYT:

It is not clear that Mr. Obama can prevail given his own diminished popularity, the tepid nature of the economic recovery and the divisions within his party. But by proposing to extend the rates for the 98 percent of households with income below $250,000 for couples and $200,000 for individuals -- and insisting that federal income tax rates in 2011 go back to their 2001 levels for income above those cutoffs -- he intends to cast the issue as a choice between supporting the middle class or giving breaks to the wealthy.