Mitt Romney celebrates his single best day of fundraising to date

— -- TROY, Mich.—Mitt Romney enjoyed what campaign officials described as his single best day of fundraising yet, taking in between $6 million and $8 million during a finance swing through Michigan on Wednesday.

"Michigan has been great," John Rakolta, a national finance co-chair of Romney's presidential campaign, told attendees during a fundraiser Romney headlined at a local Marriott here. "Today, we will exceed every single event that has been held for Gov. Romney from the beginning of the campaign. So we have set a new record tonight in terms of fundraising."

Taking the stage, Romney praised the supporters who had written checks to his 2012 bid. According to the campaign, more than 500 people contributed at least $2,500 a piece to attend tonight's reception just outside Detroit. Individuals who contributed $10,000 got to meet and pose for a photo with the Republican nominee, while $50,000 scored folks an invite to a private dinner with Romney.

"It's hard to write a check to a politician. It's harder to get a friend to do it," Romney said, praising the "herculean work" of his national finance team.

He suggested donors weren't just giving to support his campaign, but rather to get America back on track.

"I realize that this is not about me. You are not giving a check to me. You're not giving a check to the Republican Party. You are concerned about America. This is about our country. And like me, you are of the view that if we stay on the path we are on, that America will be something far less than what it could be," Romney told supporters, as they munched on appetizers. "You're trying to make an investment in America's future that will put us on the road to greatness again. And so I salute you in this mutual quest we have."

Romney's record-breaking fundraising day comes as the Obama campaign warned the president could be heavily outraised by his Republican opponent heading into the heat of the general election campaign.

Romney's Michigan swing came just after the conclusion of his five-day bus tour through six states, which ended in western Michigan Tuesday night. Romney is set to deliver a speech before the National Association of Latino Elected Officials in Orlando, Fla., Thursday, but this weekend, he turns his focus back to raising cash for his campaign, headlining a retreat for high-dollar donors to his campaign in Park City, Utah.