McCain also took a subtle dig at Obama's wife, Michelle.
"I have never lived a day, in good times or bad, that I haven't been proud of the privilege" of being an American, McCain said.
Michelle Obama has been criticized for saying, in Milwaukee, Wis., Monday, "For the first time in my adult lifetime, I'm really proud of my country and not just because Barack has done well, but because I think people are hungry for change."
In a rare move, Cindy McCain, wife of the Arizona senator, took on Michelle Obama's comment: "I'm proud of my country, I don't know if you heard those words earlier. I'm very proud of my country," she said Tuesday.
Tuesday's biggest prize was the economically struggling state of Wisconsin, which has 74 Democratic delegates at stake, and bragging rights to a state with a sizable population of blue-collar workers.
Obama's campaign argued a win in Wisconsin would quiet opponents who credited his past victories to black voters, highly educated, and high-income Democrats.
In the end, the Illinois senator challenged Clinton in some of her core support groups, trounced her on electability, and rode broad support from independents to victory in the state.
Clinton held only a single-digit lead among white women, according to exit poll results. Obama, meanwhile, prevailed by a wide margin among men.
The most striking result was Obama's huge victory among a high turnout of voters under 30; he won them by 71-25 percent.
In his speech tonight, Obama pushed back on the criticism that he is all talk and no substance.
Clinton's campaign has been busily lowering expectations in Wisconsin, and the candidate left the state Monday, preferring to hold events in Ohio.
The former first lady clearly wants her campaign — and the media — to focus on the next-up primary contests on March 4 in delegate-rich Ohio and Texas, but she did spend significant time and resources in Wisconsin.
Clinton wooed blue-collar workers with a detailed economic plan, and sent negative mailers to voters, arguing Obama's health care plan would leave millions uninsured.
The Clinton campaign also launched its first negative television ad in Wisconsin, attacking Obama in an effort to highlight his refusal to debate her in the state.
Former President Clinton and daughter Chelsea also pitched in, visiting universities and holding town hall meetings.
Publicly, the Clinton campaign argues it never expected to win in Wisconsin, but Clinton associates concede it's a tough night for the campaign, reports ABC News' Kate Snow.
"Obama will win tonight, but as more people focus on him as president and commander in chief, he's going to have a tougher and tougher race," Clinton spokesman Jay Carson told Snow.
"All you have to do is listen to Sen. McCain tonight to see that Democrats need to have a candidate with the strength and experience to take him on," Carson said.
Outside the Badger State, the Clinton campaign dispatched Chelsea Clinton to campaign for her mom in Hawaii, where 20 delegates are up for grabs.
But it was Obama, born and raised in Honolulu, who had the advantage there.
The Illinois senator's half-sister campaigned on his behalf, recording a YouTube video encouraging voters to support her brother.
The loss in Wisconsin is another blow to the former first lady, whose candidacy is now undeniably in jeopardy.