Rasmussen:

[Minnesota] Republican Sen. Norm Coleman has widened his lead over DFL challenger Al Franken, according to a telephone poll taken Tuesday of 500 likely Minnesota voters. ... 50 percent of the respondents said they favored Coleman for a second term in the U.S. Senate, while 43 percent said they backed Franken.

That's down from both March and February, when he was ahead of Coleman. In the same poll, Obama and Hillary have pulled ahead of McCain, so it's not a Democrat-fatigue-trickling-down thing. The readiest explanation I can think of is that Franken's been pestered by revelations that he was a sloppy tax-payer and might never have coughed up any California taxes on his earnings there. A surrogate told the Star-Trib Franken's tax troubles are "not a very sexy issue," but in the middle of tax season in a bad economic year, I'd bet it makes a difference.

--Eve Fairbanks