"They would govern this country in a way that will, in my opinion, take this country backward," the likely GOP nominee said this week in a speech to conservative activists that served as his opening argument for a fall showdown with either Sens. Hillary Rodham Clinton or Barack Obama.
With chief rival Mitt Romney out of the race, McCain is gearing up for the most wide-open presidential election in half a century and the first since 1960 in which a senator will win the White House.
As McCain pivots from the primary campaign to the general election, he not only must unite disaffected Republicans who view his independent streak warily but also lead a dispirited GOP against a far more energized Democratic Party.
Neither is a small task, Republicans say.
"He has between now and early November to get this worked out with conservatives. There won't be a
'big C' conservative in this country not on the campaign trail for him," said Rich Galen, a GOP strategist who advised former candidate Fred Thompson.
"The best thing that could happen is exactly what happened on the Republican side
- getting a nominee early," Galen said.
One conservative on board is Thompson, who said late Friday he was endorsing his former rival.
"This is no longer about past preferences or differences. It is about what is best for our country and for me that means that Republican should close ranks behind John McCain," Thompson said in a statement.
Said Ralph Reed, a Republican strategist and former director of the Christian Coalition: "This is the most fired up I've ever seen the liberal wing of the Democratic Party. They're hungry and they want to win. If you're John McCain and you're going into that kind of a fall campaign, you need to have the intensity, the enthusiasm and the energy of the grass roots of your party."
To that end, McCain hopes his two broad campaign pillars - national security and spending restraint
- as well as what he calls his differences with Clinton and Obama on other issues like taxes, health care and judges will bring longtime critics into the fold.
"We have profound philosophical differences. They are liberal Democrats and I am a conservative Republican," McCain frequently said of Obama and Clinton as he campaigned for the primaries
- and laid the groundwork for his fall campaign.
He often claims that a country led by either Democrat would return to a time of a bloated bureaucracy and ignored overseas threats to U.S. security.
Democrats argue that McCain represents nothing more than a continuation of the Bush presidency.
"The more voters get to know the real John McCain the more they see him for the Bush Republican he is," said Damien LaVera, a Democratic National Committee spokesman. "A vote for McCain is a vote for four more years of the same failed Bush policies that have undermined our economy and made America less secure."
