DENVER – As the Democrats prepared to open their convention Monday, top Republicans were doing all they could to stir any lingering resentment among delegates over Barack Obama’s decision not to include Hillary Rodham Clinton on the ticket.

Democrats said that the ploy wouldn’t work, that the party would leave its convention energized and united, and that Obama’s selection of Sen. Joseph R. Biden Jr. of Delaware as his running mate was proving popular throughout party ranks.

John McCain’s campaign set the terms of the day’s political conversation by unveiling a commercial suggesting that Clinton had been passed over because of her critical remarks about Obama during their long and sometimes bitter fight for the Democratic presidential nomination.

“She won millions of votes but isn’t on his ticket,” an announcer says. “Why?

“For speaking the truth.”

The ad includes clips of Clinton raising questions about the presumptive Democratic nominee and concludes: “The truth hurt, and Obama didn’t like it.”

On the Sunday talk shows, Republican spokesmen sounded the same theme.

Asked what he thought of Obama’s selection of Biden, former New York Mayor Rudy Giuliani called it a choice made out of weakness and added: “The story here is more the Obama-not-Clinton ticket.”

Said Minnesota Gov. Tim Pawlenty, a potential McCain running mate: “If I were a Hillary Clinton supporter this morning, I’d be scratching my head.”

Democrats said any effectiveness that the commercial might have would be short-lived.

Gov. Rendell predicted that Clinton’s much-anticipated speech tomorrow night “will blow this ad out of the water.”

Kansas Gov. Kathleen Sebelius, who was a finalist in the vice-presidential selection process, agreed. “Right now, I don’t think there’s any question that the Clintons are wholeheartedly behind Barack Obama,” she said.

And the Associated Press reported that Clinton was inviting her pledged delegates to a reception Wednesday, before the presidential roll call. There, in a show of support for Obama, she reportedly was planning to release her delegates from their pledges.

Obama’s aides said their man spoke to both Hillary Clinton and former President Bill Clinton by telephone late last week.

In seeking the roll call, Hillary Clinton said the event would provide “catharsis” for her most devoted supporters, many of whom are delegates. How all of this plays out will help determine how much of a problem Obama still faces in trying to bring the party together before November.

Polls are all over the lot on the question of what percentage of Clinton’s 18 million primary voters are prepared to support Obama in the fall. But the surveys indicate that at least one-third of them, and perhaps more, have yet to commit themselves, and a substantial minority say they will vote for McCain.

Monday’s opening session, which has the theme of “One Nation,” will begin to answer the question of how much emphasis the Obama team plans to put this week on fleshing out its candidate and how much on drawing the contrasts between his positions and those of his Republican opponent.

Four years ago, strategists for then-nominee John Kerry were widely criticized after the fact for having refrained from attacking their opponent, President Bush, and focusing almost exclusively on Kerry’s biography.

David Axelrod, Obama’s chief strategist, suggested that his campaign would not leave itself open to that kind of criticism in 2008. “We’re not going to shy away from making the contrast,” he said, and telling the story “of what’s happened to this country” in the last eight years.

On Night One, though, the emphasis will surely be on the Obama biography. The headline speaker is his wife, Michelle, and she will be preceded by his half-sister and his brother-in-law.

Also on the program is a tribute to Sen. Edward M. Kennedy of Massachusetts, who is suffering from brain cancer and unable to attend.

Obama’s choice for vice president, Biden, continued to be a center of attention Sunday, even though he stayed largely out of public view in Delaware.

McCain offered his own reaction to the choice. In an interview with Katie Couric of CBS News, he called it “a very wise selection” and described Biden, his longtime Senate colleague, as “a good friend and a good man.”

In honor of Biden’s prospective nomination, convention organizers moved the seats set aside for the Delaware delegation from the rear of the Pepsi Center to a prime location on the floor.

Biden is expected to arrive in Denver today and make several public appearances in the next few days before speaking to the convention Wednesday night.

Yesterday, traffic in the downtown area was occasionally disrupted by about 1,000 peaceful antiwar demonstrators who marched through the city streets.

They waved signs and chanted: “Stop the torture, stop the war. That’s what we’re fighting for.”

Giuliani and Axelrod spoke on ABC’s “This Week, Rendell and Sebelius on CBS’s “Face the Nation. Pawlenty was interviewed on CNN’s “Late Edition.