Speaking to an audience of Hispanic military veterans, McCain stepped up his criticism of Obama while the Illinois senator continued his headline-grabbing tour of the Middle East and Europe. The Arizona Republican contended that Obama's policies - he opposed sending more troops to Iraq in the "surge" that McCain supported would have led to defeat there and in Afghanistan.
"We rejected the audacity of hopelessness, and we were right," McCain said, a play on the title of Obama's book "The Audacity of Hope."
McCain laid out a near-apocalyptic chain of events he said could have resulted had Obama managed to stop the troop buildup ordered by President Bush: U.S. forces retreating under fire, the Iraqi army collapsing, civilian casualties increasing dramatically, al Qaeda killing cooperative Sunni sheiks and finding safe havens to train fighters and launch attacks on Americans, and civil war, genocide and a wider conflict.
"Above all, America would have been humiliated and weakened," he said. "Terrorists would have seen our defeat as evidence America lacked the resolve to defeat them. As Iraq descended into chaos, other countries in the Middle East would have come to the aid of their favored factions, and the entire region might have erupted in war."
Noting that the buildup was unpopular with most Americans, McCain said: "Sen. Obama told the American people what he thought you wanted to hear. I told you the truth."
"Sen. Obama said this week that even knowing what he knows today that he still would have opposed the surge. In retrospect, given the opportunity to choose between failure and success, he chooses failure. I cannot conceive of a Commander in Chief making that choice."
The Obama campaign said McCain's "false accusations" would not add to the debate over the Iraq war.
"Barack Obama and John McCain may differ over our strategy in Iraq, but they are united in their support for our brave troops and their desire to protect this nation," said Obama spokesman Bill Burton. "Sen. McCain's constant suggestion otherwise is not worthy of the campaign he claimed he would run or the magnitude of the challenges this nation faces."
Obama has called for a withdrawal over 16 months. McCain again criticized him for advocating "a politically expedient timetable" and for voting against funding for troops. McCain had raised eyebrows earlier this week by charging that Obama "would rather lose a war in order to win a political campaign."
With once exception, Obama has voted for every spending bill for troops at war. In 2007, Bush vetoed a bill that provided funding on condition of troop withdrawals, and Obama joined 13 other senators who opposed the measure that took its place.
McCain's speech in Denver came at the conclusion of a week in which he struggled against Obama's overseas tour de force. Yet amid the awkward moments, McCain managed to campaign busily in key battleground states and to raise millions of dollars at fundraisers.
Polls in many swing states are close, and some are tightening. The Arizona Republican sought to turn this to his advantage in what was clearly a difficult week to be a stay-at-home candidate.
McCain repeatedly emphasized his long military and congressional background, scolded Obama from afar on foreign policy, and kept playfully fueling speculation that he was close to picking a running mate. His address to the group of Hispanic veterans also gave him a chance to court the valued Hispanic vote.
Veterans care has been an issue that has come up numerous times at recent town halls McCain has held, reports CBS News' John Bentley, and the Arizona senator reaffirmed his commitment to getting soldiers appropriate treatment.
McCain was to visit the Dalai Lama in Aspen, Colo., his first meeting with the Tibetan spiritual leader and a chance to express criticism of Chinese treatment of those who live in Tibet just weeks before the Olympics in Beijing.
McCain also was to spend the weekend in Arizona and make a round of television news shows on Sunday.
Everywhere he went in recent days - in New Hampshire, Maine, Pennsylvania, Ohio and here in Colorado - the Arizona senator drew warm and appreciative crowds. No matter that many, if not most, of those in the audiences were senior citizens. Seniors vote in big numbers.
For the most part, the side-by-side images weren't pretty:
Obama meeting with leaders in Iraq, McCain on a golf cart in Kennebunkport, Maine, with the first President Bush.
Obama before a sweeping Mideast landscape, McCain holding a news conference in a supermarket in Bethlehem - Pennsylvania, that is - and narrowly escaping an attack from a tumbling stack of apple sauce jars.
Obama delivering his trip's keynote speech at Berlin's Victory Column, McCain eating bratwurst and chatting with reporters at a German restaurant in Columbus, Ohio.
McCain responds philosophically when asked about being overshadowed by his rival's overseas trip and outsize attention: "It is what it is."
McCain has inched ahead of Obama in Colorado, come within inches in Minnesota and narrowed the gap in Michigan and Wisconsin, according to Quinnipiac University polls of likely voters in these battleground states. The polls, taken for The Wall Street Journal and washingtonpost.com, showed voters in each state saying energy policy is more important than the war in Iraq.