Some Democrats see the risk of having one candidate

“It plays into the old Clinton narrative, which isn’t the best way to get her [campaign] kicked off here,” said Joe Judge, chairman of the Monroe County Democratic Party in Iowa. “Campaigns can be nasty things, and it would not surprise me if someone brought it up.’’

Mr. Brown of South Carolina, who is considering supporting Mr. O’Malley, said that Mrs. Clinton’s Tuesday news conference presented a style that won’t wear well on the campaign trail.

“Her approach to it was flip, arrogant and I think at the end of the day it underlines the fact that she lives in this world where she is going to call her own shots and live by her own rules,” said Mr. Brown. “That’s not good for our party going forward.”