Another Democrat will jump into the race to challenge U.S. Sen. Chuck Grassley in 2010, and that candidate will give Iowa’s senior senator “the race of his life,” Iowa Democratic Party Chairman Michael Kiernan said.

The news comes on the heels of evidence that Grassley could be vulnerable to a challenge from a well-known Democrat.

Rumors have been circulating about a possible another candidate, with deep pockets and high name recognition, jumping into the senatorial primary. But over the past few months, all names associated with the race, from former Principal CEO Barry Griswell to Iowa Power Fund Chair Fred Hubbell, have denied interest.

At a Friday afternoon taping of IPTV’s “Iowa Press,” Kiernan said the rumors of another candidate are true, although he declined to say who it will be.

From a report at Radio Iowa:

“Doug Gross has gone and pulled out of retirement Terry Branstad to run for governor so it got a lot of Democrats thinking, including myself, ‘Maybe it’s time,’ — and I’ll put this in a football analogy since my counterpart (the chairman of the Republican Party of Iowa) owns a football team, that ‘Maybe it’s time to get a first-round draft pick,” Kiernan says.  “I’m going to tell you here today that Chuck Grassley is going to be in for the race of his life.”

He later said that the mystery candidate is 100 percent committed to entering the race, but will wait until after former Gov. Terry Branstad announces he will run for the GOP gubernatorial primary to reveal their intentions.

Bob Krause of Fairfield, Tom Fiegen of Clarence and Sal Muhammad of Sioux City are currently seeking the Democratic nomination to take on the six-term senator.