With voting underway on Tuesday, polls indicated that Kerry was set for a strong performance against his Democratic rivals.
A former Vietnam veteran, Kerry has already won the primaries in Iowa and New Hampshire.
Closing out a six-day swing through all seven states, Kerry however struck a cautious note, saying that a national poll showing he could topple President Bush made for a "great headline" but "doesn’t mean a lot in terms of the long haul here."
At a concluding rally in an airport hangar in Spokane, Washington, Kerry was energized and eager to get to challenge Bush.
"If you will join me in this fight I pledge to you that every day as president I will stand up for common sense and mainstream American values and together on 2 November we can send George Bush back to Texas," he said.
Besides Missouri and Arizona, voting is taking place in South Carolina, Oklahoma, New Mexico, North Dakota and Delaware.
A Detroit News poll in Michigan, which votes on Saturday, had Kerry leading the one-time front-runner Howard Dean 56% to 13% among likely voters in the state.
A USA Today/CNN/Gallup poll had him defeating Bush 53% to 46%, a lead outside the poll's margin of error.
The survey of likely voters taken Thursday through Sunday said it reflected the battering Bush has taken and the questions raised in the past week over the administration's rationale for going to war with Iraq.