BRIDGEPORT, Conn. - President Barack Obama implored voters on Saturday to resist a Republican tide, warning that if the GOP prevails in Tuesday's midterm elections all the progress of his first two years in office "can be rolled back."

That would be just fine, said Rep. John Boehner, in line to become the new speaker if Republicans take the House, as expected. He declared, "Americans are demanding a new way forward in Washington."

Embarking on a four-state weekend campaign dash, Obama acknowledged the difficulties Democrats face - the distinct chance of losing their comfortable majority in the House and possibly the Senate, as well as several governors' seats.

All four weekend stops are in states Obama carried in 2008 - Pennsylvania, Connecticut, Illinois and Ohio. But Democratic candidates for the Senate, House and governorships are struggling in these places and elsewhere, and Obama is making a last-ditch plea for the party's core supporters not to abandon them.

"It is difficult here in Pennsylvania, it is difficult all across the country," Obama told several hundred campaign volunteers at Temple University in Philadelphia, a Democratic-leaning city he has visited often.

The weekend tour marks the president's last campaign swing of the election season, with Republicans expecting big victories on Tuesday. Obama's sagging popularity has limited his ability to save Democratic candidates, and his legislative agenda may be deeply complicated if the GOP takes over the House, as many expect.

Unless Democratic voters turn out in big numbers, Obama said in a seven-minute talk, all the progress made in the past two years "can be rolled back."

Several of Pennsylvania's U.S. House Democrats are battling for survival, as is the Senate nominee, Joe Sestak.

Republicans expect to win the governor's seat, as two-term Democratic Gov. Ed Rendell is term-limited.

Democratic prospects appear somewhat better in Connecticut, Obama's second stop. The party has high hopes for Senate nominee Richard Blumenthal and gubernatorial candidate Dan Malloy, although neither race is considered in the bag.

But freshman Rep. Jim Himes faces a tough challenge from Republican Dan Debicella, and organizers allowed Himes to introduce Obama to loud applause from more than 9,000 people at the Bridgeport Arena.

Obama urged Democrats to "defy the conventional wisdom" that foresees huge GOP wins.

"There's no doubt this is a tough election," he said, "because we have been through an incredibly difficult time as a nation."

In his two appearances, Obama did not mention the thwarted mail bomb plot or the arrest in Yemen of a woman suspected of sending two mail bombs.

Obama planned an evening rally in Chicago, his home town. He is to headline a final rally today in Cleveland before returning to Washington for Halloween with his family.

In his weekly radio and Internet address, Obama said it's time to put aside partisanship. But his appeal for unity included jabs at GOP leaders for comments he called troubling.

Boehner, currently the House minority leader, "actually said that 'this is not the time for compromise,'" Obama said. He said Senate Minority Leader Mitch McConnell of Kentucky "said his main goal after this election is simply to win the next one."

"I know that we're in the final days of a campaign," Obama said in his weekly address. "So it's not surprising that we're seeing this heated rhetoric. That's politics. But when the ballots are cast and the voting is done, we need to put this kind of partisanship side - win, lose or draw."

Boehner, in the weekly Republican radio address, said Obama has failed to deliver the change he promised - and American workers have lost jobs as a result of White House policies. The Ohio Republican spoke up for a GOP pledges to cut spending and keep taxes at current levels.

"This is a new way forward that hasn't been tried in Washington yet," Boehner said. "It's a break from the direction in which President Obama has taken our country."

"And frankly, it's also a break from the direction in which Republicans were headed when Americans last entrusted us with the reins of government. The American people are in charge, and they deserve nothing less."

Candidates were everywhere on Saturday, making last-weekend pitches for support.

Party stars were out in force, too.

Former President Bill Clinton, campaigning for Ohio Gov. Ted Strickland's re-election, called the Republican pledge "a joke." He said, "Their deal sounds good but it doesn't work. ... Our ideas work better than theirs."

Later in Canton, Ohio, as Clinton was speaking at a rally, Ohio Rep. John Boccieri ran offstage after receiving word that his pregnant wife had gone into labor.

"The baby is now being born!" Clinton announced as the crowd erupted with cheers. "We got another Democrat."

Sarah Palin and her husband, Todd, campaigned for Republican Senate candidate John Raese at a big rally in Charleston, W.Va. Palin said the state's Democratic governor, Joe Manchin, is a good fit in that job - so voters should keep him there rather than elect him senator over Raese.

In many races, vast numbers of the electorate had already made their choices. In Ohio, where Democrats could lose as many as six House seats, more than 721,000 votes had been cast. California officials already had in hand almost 2.5 million ballots, and Florida officials had almost 1.7 million.

Both parties worked vigorously to bank supporters' votes early. In all, more than 13.5 million votes had been cast early, either at ballot boxes that opened early or by mail. Four years ago, during the last non-presidential election, some 19 million voters cast ballots before Election Day.

Obama met mostly adoring crowds Saturday. But protesters seeking more money to fight global AIDS interrupted his Connecticut speech. The president told them they should be protesting at GOP events because "we're funding global AIDS, and the other side is not."