Democrat Barack Obama challenged his Republican opponent John McCain on Tuesday to stop questioning his "character and patriotism."

Addressing the Veterans of Foreign Wars convention, Obama reaffirmed his early opposition to the U.S. invasion of Iraq and said the so-called "surge" strategy of sending 30,000 additional troops to Iraq last year had not produced the political reconciliation necessary to achieve lasting peace in the country. McCain supported the Iraq invasion and was an early champion of the surge.

"Yesterday, Sen. McCain came before you. He is a man who has served this nation honorably, and he correctly stated that one of the chief criteria for the American people in this election is going to be who can exercise the best judgment as Commander in Chief," Obama said. "But instead of just offering policy answers, he turned to a typical laundry list of political attacks. He said that I have changed my position on Iraq when I have not. He said that I am for a path of "retreat and failure."

"These are the judgments I've made and the policies that we have to debate, because we do have differences in this election," Obama said. "One of the things that we have to change in this country is the idea that people can't disagree without challenging each other's character and patriotism. I have never suggested that Sen. McCain picks his positions on national security based on politics or personal ambition. I have not suggested it because I believe that he genuinely wants to serve America's national interest. Now, it's time for him to acknowledge that I want to do the same.

"Let me be clear: I will let no one question my love of this country," Obama said to applause.

McCain stood before the same audience a day earlier and said Obama "tried to legislate failure" in the Iraq war and had put his ambition to be president above the interests of the United States. He said the Illinois senator did this by pushing for a timetable for withdrawal of U.S. combat troops from Iraq and by voting in the Senate against a major appropriations bill to help fund the troop increase.

"With less than three months to go before the election, a lot of people are still trying to square Sen. Obama's varying positions on the surge in Iraq. First, he opposed the surge and confidently predicted that it would fail. Then he tried to prevent funding for the troops who carried out the surge," McCain said.

"Not content to merely predict failure in Iraq, my opponent tried to legislate failure."

Obama has acknowledged the surge reduced violence in Iraq but says it has failed in the goal, stated by the White House, of facilitating reconciliation among contentious Iraqi factions.

However, the Iraqis themselves are seeking specific timelines for a U.S. troop withdrawal. Iraq's president, Nouri al-Malaki, and national security adviser, Mouwaffak al-Rubaie, have both said their country would not accept any deal for a prolonged U.S. presence in Iraq unless the agreement sets specific dates for the withdrawal of U.S.-led forces.

McCain has also spoken out strongly against Russia's invasion of the Republic of Georgia, using Obama's absence from the campaign trail last week when he was on vacation in Hawaii to take a hard line against the Russian government. His tough talk led some of Obama's foreign policy advisers to suggest McCain may have complicated the conflict.

Obama strongly condemned Russia's actions Tuesday but said the U.S. involvement in Iraq had imperiled U.S. ability to take a leadership role in the matter.

"If we think that we can secure our country by just talking tough without acting tough and smart, then we will misunderstand this moment and miss its opportunities," Obama said. "If we think that we can use the same partisan playbook where we just challenge our opponent’s patriotism to win an election, then the American people will lose. The times are too serious for this kind of politics. The calamity left behind by the last eight years is too great."