GREENWOOD VILLAGE -- Standing in the bed of a black pickup truck, megaphone in hand, former Massachusetts Gov. Mitt Romney blasted Democratic presidential nominee Barack Obama's tax plan Saturday night.

"Barack Obama said he was only going to only raise taxes on people earning over $250,000," Romney said to a group of Republican volunteers outside John McCain's Colorado state headquarters. "And then he slipped up and said, no, $200,000. And then Joe Biden slipped up and said, no, 150,000. And then I understand that Governor Richardson slipped up yesterday and said $125,000."

"Do I hear 80, Do I hear 70?" Romney said auctioneer-style, drawing laughter and cheers.

Romney said under an Obama administration, America would "take a sharp left ...down the pathway Barack Obama and the Europeans have gone."

"(Obama) wants to make it more difficult for us to trade with other nations," Romney said. "He wants to have an energy policy that doesn't use as it should our nuclear and coal and offshore drilling resources."

Romney, on the truck with former Republican Colorado Gov. Bill Owens, also offered a depreciating story about himself when he attended the Summer Olympics this year in Beijing.

The crowd, he said, "reminded me of the time I went to the women's beach volleyball game in Beijing."

Sitting in the front row of a USA women's beach volleyball game with his wife Ann -- " Ann was the one that insisted I go to that," he added - Romney said he noticed some Americans in the stands.

"And then they started to point over at me and they took out their cameras, were taking my picture. And then I noticed some Chinese were doing the same thing. Yeah, they were taking out their cameras pointing at me," Romney said. "I thought, ‘Ann can you believe this? These people here seen my campaign all the way across the world?

"And so I started feeling pretty good about myself. I said, ‘Sweetheart, you better stand up or sit up straight -- they're taking our picture.'

"And she goes like this," Romney said, pointing his thumb behind him.

"And I turn around and there's Kobe Bryant sitting there," Romney said to laughter. "So Bill Owens and I know when our time is come and gone."

Romney was originally scheduled to speak in McCain's headquarters, but the large crowd that gathered quickly heated up the office to the point that Romney spoke outside.

"The heat was moving up, and I was thinking to myself, ‘This must be what Obama health care is going to be like,'" said Republican U.S. Senate nominee Bob Schaffer, who spoke after Romney.

"Now we're out here in the fresh air where we're all happy and cooler, this is what McCain health care is like," Schaffer said.