DENVER – Barack Obama promised a clean break from the “broken politics in Washington and the failed policies of George W. Bush” Thursday night as he embarked on the final lap of his audacious bid to become the nation’s first black president.

He vowed to cut taxes for nearly all working-class families, end the war in Iraq and break America’s dependence on Mideast oil within a decade. By contrast, he said, “John McCain has voted with President Bush 90 percent of the time,” a scathing indictment of his Republican rival – on health care, education, the economy and more.

Polls indicate a close race between Obama and McCain, the Arizona senator who stands between him and a place in history. On a night 45 years after Martin Luther King Jr. delivered his “I have a Dream Speech,” Obama made no overt mention of his own race.

“I realize that I am not the likeliest candidate for this office. I don’t fit the typical pedigree” of a presidential candidate was as close as he came to the long-smoldering issue that may well determine the outcome of the election.

Campaigning as an advocate of a new kind of politics, he suggested at least some common ground was possible on abortion, gun control, immigration and gay marriage.

Obama and his running mate, Sen. Joseph Biden of Delaware, leave their convention city on Friday for Pennsylvania, first stop on an eight-week sprint to Election Day.

McCain countered with a bold move of his own, hoping to steal some of the political spotlight by spreading word that he had settled on a vice presidential running mate. Minnesota Gov. Tim Pawlenty canceled all scheduled appearances for the next two days, stoking speculation that he was the one.

Rep. John Lewis of Georgia spoke first of the anniversary of King’s memorable speech.

“Tonight we are gathered here in this magnificent stadium in Denver because we still have a dream,” said the Georgia lawmaker, who marched with King, supported Obama’s primary rival, Hillary Rodham Clinton, then switched under pressure from younger black leaders in his home state and elsewhere.

In his speech, Obama pledged to jettison Bush’s economic policy – and replace it with his own designed to help hard-pressed families.

“I will cut taxes for 95 percent of all working families. Because in an economy like this, the last thing we should do is raise taxes on the middle class,” he said.

The speech didn’t mention it, but Obama has called for raising taxes on upper-income Americans to help pay for expanded health care and other domestic programs.

He did not say precisely what he meant by breaking the country’s dependence on Mideast oil, only that Washington has been talking about doing it for 30 years “and John McCain has been there for 26 of them.”

His pledge to end the war in Iraq responsibly was straight from his daily campaign speeches.

“I will rebuild our military to meet future conflicts. But I will also renew the tough, direct diplomacy that can prevent Iran from obtaining nuclear weapons,” he added.

As he does so often while campaigning, Obama also paid tribute to McCain’s heroism – the 72-year-old Arizona senator was a prisoner of war in Vietnam – then assailed him.

“Sen. McCain likes to talk about judgment, but really, what does it say about your judgment when you think George Bush was right more than 90 percent of the time?