More than 400 people crowded into U.S. Senate candidate Tim Kaine’s new Richmond headquarters on a cold, dreary Sunday afternoon as the campaign officially opened its doors.

(Courtesy Kaine campaign)

“This is going to be razor thin, very close, that call you make, that door you knock on might be the one,’’ he said.

Kaine, dressed casually in jeans and a sweater, was joined by his wife, former judge Anne Holton; Lindwood Holton, his father-in-law and former Republican governor, state legislators and Democratic activists.

Kaine said he would work to pick up where retiring Sen. Jim Webb (D) left off on military and veteran issues, and he spoke about the need of expanding educational opportunities and welcoming people to the state.

“What moved us was talent, what moved us was education...we grow our own talent, we attract our own talent,’’ he said.

Kaine promised to run a positive, forward looking campaign. Two others — Julien Modica, a health-care company executive, and Courtney Lynch, founding partner of a consulting firm — are running in the Democratic primary.

Kaine never mentioned Allen — a former governor and senator — by name, but criticized him for his role in turning record surpluses into record deficits.

The crowded Republican field also includes Del. Bob Marshall (Prince William), Jamie Radtke, former chairwoman of the Virginia Federation of Tea Party Patriots; Hampton Roads lawyer David McCormick; and Bishop Earl Jackson.

“When I hear my opponents say ‘I’m going to take America back,’ I say back from who?’’ Kaine said. “I reject any doom and gloom notion about this nation.’’

Kaine’s campaign has been collecting signatures to get on the June ballot. He said he does not support changing ballot requirements, despite the difficult time some presidential candidates had, but that he wants to make sure everyone has to abide by the same rules.

Update, 9 pm: Allen spokesman Bill Riggs responded to Kaine’s criticisms.

“It’s disappointing that Chairman Kaine didn’t have the same concern for deficits when he was in Washington championing through an explosion of government spending that made annual trillion dollar deficits the norm and added $4.6 trillion to the national debt,” he said. ”The truth is Tim Kaine has supported every significant policy to come out of Washington in the last three years and no amount of partisan political-speak is going to convince Virginians that he won’t be just another rubber-stamp for President Obama and his Washington allies.”