Tom Vilsack has ruled out running for U.S. Senate in 2014, clearing the way for the early Democratic frontrunner, U.S. Rep. Bruce Braley, to press forward and raise money for what's expected to be one of the most fiercely competitive races in the country.

"He will not seek the open seat," Matt Paul, a longtime Vilsack aide, told The Des Moines Register this morning.

U.S. Sen. Tom Harkin, a 73-year-old Democrat, announced in late January that he intends to retire in two years after 40 years in Congress.

The Register's most recent Iowa Poll stirred up buzz about a possible Senate bid by Vilsack, a former Iowa governor who is now a member of President Barack Obama's cabinet. The Feb. 3-6 poll shows 56 percent of Iowans say they think Vilsack would be an appealing Senate candidate, while 35 percent say he wouldn't be.

Of eight buzzed-about names the Register tested, only Vilsack, who has been U.S. secretary of agriculture since 2009, earns majority support.

Although Vilsack's name always appears on short lists of possible Senate nominees, he hadn't publicly stated interest. But he hadn't knocked down the idea, either - until now.

This morning, Paul said Vilsack is focused on his job as agriculture secretary.

Vilsack, 62, oversees a $147 billion budget, 100,000 employees and offices in every state and 80 countries. In mid-January, Obama asked Vilsack to stay on and Vilsack accepted.

Because Iowa hasn't had an open U.S. Senate race since 1974, nominations are considered a rare prize. The race already is driving intense competition and heavy national attention. Given Iowa's status as a purple state, where neither party has an advantage, it's expected to be one of the three hottest races in 2014.