DES MOINES, Iowa » Despite Sen. John McCain's prediction of an upset, Sen. Barack Obama reached for a landslide yesterday, 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.

McCain charged that the Hawaii-born 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.

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 Illinois 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 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.

After a stop home in Chicago to share Halloween with his two daughters, Obama took a bus ride about 30 miles across the state border, capping his day with a rally in Highland, Ind. “;We are four days away from changing the United States of America,”; he proclaimed to a cheering crowd.

Indiana is one of about a half-dozen states that went for President Bush twice but remain up for grabs late this election season. Bush won the state by a 60-39 percent margin in 2004.

Aides announced Obama would air television commercials in McCain's home state of Arizona as well as in North Dakota and Georgia. He had run ads in the latter two states earlier in the campaign before suspending that effort.

McCain was on the second day of a bus tour through battleground Ohio, a state that supported Bush and has voted with the winner in each presidential election for two decades.

“;We're closing, my friends, and we're going to win in Ohio. We're a few points down but we're coming back and we're coming back strong,”; he said.

Later yesterday, Schwarzenegger joined him at a rally in Columbus. “;John McCain has served his country longer in a POW camp than his opponent has in the United States Senate,”; he said. “;I only play an action hero in the movies. John McCain is a real action hero.”;

In a new television ad, McCain pledged to fix the economy, cut government waste and safeguard the nation's security.