"My Republican opponent won't be able to say that we both supported the war in Iraq, because I didn't," Obama told a crowd packed into a high school gym.
"My opponent won't be able to say that I haven't been open or straight with the American people or that I've flipped and flopped my positions, because I haven't. I've been consistent this whole time."
The Illinois senator added to his argument his opposition to a recent Senate resolution branding Iran's Revolutionary Guard a terrorist organization. He described the resolution as a step toward another war. He did not vote against the measure when it came up in the senate because he was campaigning in New Hampshire.
"My Republican opponent won't be able to say that, 'Well, we really agree about using the war in Iraq to justify military action against Iran, or about a diplomacy of not talking and saber-rattling, because I don't agree with those approaches," he said.
Obama's remarks appeared pointed at his top rival, Sen., the only Democratic candidate to vote for the resolution. The New York senator also voted to authorize the war in Iraq. Obama was not in the Senate at the time of the vote, but as a candidate running for Senate said that he opposed the war.
Obama did not note Clinton's support of either measure or mention her by name in his remarks.
The senator did take direct aim at the White House, noting President Bush's recent comment that if Iran could make nuclear weapons, it could lead to World War III.
"This kind of 'bring it on' rhetoric is dangerous, it's irresponsible, it leads directly to the increased threat from Iran and America's decreased ability to leave the war," Obama said.
The White House has said the comment was only meant to be rhetorical.
Obama's stop in Nevada was his first in six weeks. The state has drawn increased attention from presidential candidates since Democrats allowed it to hold one of the earliest nominating contests.
Obama began his day in Reno, where he held a large rally and delivered similar remarks. He told the crowd there that President Clinton's attempt to reform health care in 1993 failed partly because Hillary Clinton, then first lady, worked only with "her own people" and shut out other potential allies.
Hilarie Grey, spokeswoman for Clinton's campaign in Nevada, said that unlike Obama, Clinton has a plan to deliver universal health care and is the "candidate that voters trust the most to end the war in Iraq."
"Its unfortunate that Senator Obama is abandoning the politics of hope and instead employing the same old attack politics as his campaign stalls. Nothing says politics as usual more than that," she said.