Republican Joni Ernst has a 6-point lead over Democratic Rep. Bruce Braley in the race in Iowa to replace retiring Democratic Sen. Tom Harkin, said a poll released Wednesday.
Republican Joni Ernst up 6 points in Iowa Senate race: poll →
Mr. Harkin said that Mr. Biden, Maryland Gov. Martin O'Malley, Sen. Mark R. Warner of Virginia and Mr. Sanders could also run for the Democratic nomination.
Hillary Clinton returns to Iowa, teases about 2016 White House ambitions →