Greg makes the excellent point that Obama ran on exactly this issue back in 2008 and seemed to do okay, really. What I'll add is that whatever Bai believes about "historical narratives left over from the 20th century," it's also the case that Bill Clinton in ran on higher taxes for rich people (and a middle class tax cut) back in 1992, and once again seemed to survive it somehow. Here's the deficit paragraph from the 1992 platform, which shouldn't seem entirely unfamiliar:
Addressing the deficit requires fair and shared sacrifice of all Americans for the common good. In 12 Republican years a national debt that took 200 years to accumulate has been quadrupled. Rising interest on that debt now swallows one tax dollar in seven. In place of the Republican supply-side disaster, the Democratic investment, economic conversion and growth strategy will generate more revenues from a growing economy. We must also tackle spending, by putting everything on the table; eliminate nonproductive programs; achieve defense savings; reform entitlement programs to control soaring health care costs; cut federal administrative costs by 3 percent annually for four years; limit increases in the "present budget" to the rate of growth in the average American's paycheck; apply a strict "pay as you go" rule to new non-investment spending; and make the rich pay their fair share in taxes. These choices will be made while protecting senior citizens and without further victimizing the poor. This deficit reduction effort will encourage private savings, eliminate the budget deficit over time, and permit fiscal policies that can restore America's economic health.I'll also agree with Greg's caveat...it's quite possible that the polling that shows tax increases on the rich isn't predictive. And I'll add that it's also certainly possible that Clinton in 1992 and Obama in 2008 would have won by even more had they only changed that particular plank. But then again one could certainly argue -- and back it up with some evidence -- that Republicans have as much of a continuing problem of being seen as the party of the rich as Democrats have with being the party of higher taxes.
The other half of this is that when we're talking budget, there are always trade-offs. Especially for politicians who have already been elected and have to submit their plans to CBO. Even if it's true that there are risks for Obama in advocating tax increases for the wealthy, if he did not do that he'd have to be behind steeper cuts to (very possibly) popular programs, or higher taxes on middle-class people, or larger deficits. Each of which, presumably, has risks as well.