Despite John McCain's prediction of an upset, Barack Obama reached for a landslide Friday, invading his rival's home state with TV ads and building a lead in early voting in key battlegrounds as the presidential race headed into a hectic final weekend.

Republican presidential candidate Sen. John McCain, R-Ariz. right, acknowledges his supporters as he arrives with California Gov. Arnold Schwarzenegger at a rally Friday, October 31, 2008, at the Nationwide Arena in Columbus, Ohio. [Agencies]

McCain charged that Obama, bidding to become the first black president, "began his campaign in the liberal left lane of politics and has never left it. He's more liberal than a senator who calls himself a socialist," he added in Hanoverton, Ohio, a reference to Sen. Bernie Sanders, an independent from Vermont.

Yet with the economy almost certainly in a recession and the country clamoring for change after eight years of Republican rule, even some of McCain's allies conceded the obvious. California Gov. Arnold Schwarzenegger said it would take a "major struggle for him to win" -- although he quickly added the Arizona senator had come back before when he had been counted out.

Privately, McCain's aides said their man trailed Obama by 4 points nationwide in internal polling.

An Associated Press-Yahoo News poll of likely voters put the Democrat ahead, 51 to 43, with a margin of error of plus or minus 3 percentage points.

The same survey gave McCain reason to hope – one in seven voters, 14 percent of the total – said they were undecided or might yet change their minds.

While the race for the White House drew most of the attention, minority Republicans in Congress braced for the loss of more seats in both the House and Senate.

Some said fresh polling in North Carolina suggested that incumbent GOP Elizabeth Dole had fallen further behind since airing an ad that tried to tie Democratic rival Kay Hagan to atheists.

Four days before the election, Obama was expanding his reach, and drawing large crowds as he moved methodically from one state to another that voted Republican in 2004.