Speaking after his win in Wisconsin, Obama said on Tuesday: "The change we seek is still months and miles away, and we need the good people of Texas to help get us there."
The Illinois senator split the support of white women almost evenly with the former first lady and did well among working class voters in the Midwestern state to cut deeply into Clinton's support, polling place interviews indicated.
McCain victories
McCain, the Arizona senator, now holds an almost insurmountable lead in delegates over Republican rivals Mike Huckabee and Ron Paul.
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"Thank you Wisconsin for bringing us to the point where even a superstitious naval aviator can claim with confidence and humility that I will be our party's nominee for president," McCain, a former Navy fighter pilot and Vietnam prisoner of war, told supporters in Columbus, Ohio.
In his victory remarks on Tuesday, McCain took direct aim at Obama.
"I will fight every moment of every day in this campaign to make sure that Americans are not deceived by an eloquent but empty call for change," the Republican nominee-in-waiting said in a thinly veiled attack on Obama's campaign slogan.
Obama targeted
His words seemed to echo Clinton's, who all but conceded Wisconsin even before the release of results.
Addressing supporters, Clinton, senator for New York, never mentioned her Wisconsin loss and instead attacked Obama's oratory as empty and meaningless.
The primary campaign "is about picking a president who relies not just on words but on work - on hard work to get America back to work", she told a Youngstown, Ohio, rally on Tuesday night.