Both major party presidential campaigns surfaced in the Twin Cities on Thursday, the most recent evidence that they expect Minnesota to be a battleground state in the November election.

In the morning, to mark the 73rd anniversary of the establishment of Social Security, the Minnesota campaign of presumptive Democratic nominee Barack Obama brought out several state DFL party elders to launch a grass-roots program designed to promote Obama to senior citizens.

In the evening, the campaign of presumptive Republican nominee John McCain held about 100 house parties across the state, part of a nationwide effort to organize supporters at the grass-roots level.

Obama's "Seniors Talking to Seniors" program will involve phone banking and person-to-person contacts by Minnesota senior citizens with others to promote Obama's plans to protect Social Security and to make affordable health care available.

"What the Republicans have found is that a direct attack on Social Security or direct attack on Medicare is worth their political life," said former Vice President Walter Mondale, making his most prominent appearance to date for Obama. "It's the third political rail. What they want to do is bleed it to death."

Asked why Obama and McCain appeared to be so close in polls, Mondale said, "It's trash time and a lot of decent people think where there's smoke there's fire. And the way to cut through that smoke is to talk to each other."

The McCain house parties included a conference call by Cindy McCain and a senior campaign aide, answering questions about the race.

"It's a chance to sign up volunteers, get lawn signs, get your neighbors to be part of the process," said McCain spokesman Tom Steward.

MARK BRUNSWICK AND Bob von Sternberg