According to this news story, Wendy Rosen, the Democratic nominee for U.S. House, Maryland First District, is withdrawing from the race. However, the deadline has passed for her to remove her name from the November ballot. The First District is a swing district. The district elected a Democrat in 2008 but a Republican in 2010. The boundaries of the district are somewhat different this year than they were in 2012. Thanks to Thomas Jones for the link.
UPDATE for September 11: the Democratic Party will choose a write-in candidate, because the party feels it can’t ask voters in the district to vote for Rosen. The last time a major party got behind a write-in candidate for U.S. House was in Texas in 2006, in the 22nd district. Shelley Sekula Gibbs was the endorsed Republican choice. She polled 61,938 write-ins, a very good total for a write-in candidate, but she lost to the Democrat, Nick Lampson, who received 76,775 votes. Tom Delay had been permitted to withdraw so there was no Republican candidate listed on the ballot. In the current Maryland race, Wendy Rosen remains on the ballot, so the Democratic vote will be split.