President Bush and Sen. John Kerry both sought political advantage Saturday from taped warnings by Osama bin Laden, jousting over how they would protect the country as they raced around the upper Midwest on the closing weekend of one of history’s most bitter presidential campaigns.

The tape, which surfaced late Friday, introduced yet another uncertainty into the election for both campaigns as they headed into a 72-hour sprint that they had thought would be dominated by more traditional last-minute appeals to voters.

Kerry attempted to stick to his strategy of criticizing Bush on the economy, and it was clear his aides did not want the tape to dominate the closing days of the campaign. Bush’s advisers said the tape refocused attention on his strong suit and provided relief from a spate of troublesome news stories that beset him last week.

After an intense internal debate, the Bush administration announced in the afternoon that it was leaving the national terrorism threat level unchanged. But in a move that some Democrats branded as a new example of White House fear-mongering, the FBI and the Department of Homeland Security sent a memo late Friday to local and state officials warning them that the federal government “cannot discount the possibility that the video may be intended to promote violence or serve as a signal for an attack.”

Echoing a line from the finale of his father’s 1992 re-election campaign, Bush told a crowd in an arena next to Lambeau Field in Green Bay, Wis., “In less than 72 hours, the American people will be voting, and the decision comes down to who do you trust?”

Kerry wanted to close his campaign by focusing on the plight of the middle class. But at a morning rally in Appleton, Wis., the Massachusetts senator renewed his attack on Bush for letting bin Laden slip through his hands.

“As I have said for two years now, when Osama bin Laden and al-Qaida were cornered in the mountains of Tora Bora, it was wrong to outsource the job of capturing them to Afghan warlords,” Kerry said. “It was wrong to divert our forces from Afghanistan so we could rush to war with Iraq without a plan to win the peace.”

Kerry had dropped the line after the tape aired Friday, but he reinserted it Saturday. In an emotional pitch to women and independents, Kerry said that when the spouses of service members deployed in Iraq go to the polls on Tuesday, “they’re going to wonder whether or not we can afford four more years of a president who is unwilling to admit any mistake.”

Bush reminded cheering supporters at a rally in Michigan – a state that looked safe for Kerry but has become a final-weeks battleground – that Americans will go to the polls “in a time of war and ongoing threats unlike any we have faced before.”

“The terrorists who killed thousands of innocent people are still dangerous, and they are determined,” Bush said in Grand Rapids. “The outcome of this election will set the direction of the war against terror.”

Around lunchtime, the Bush-Cheney campaign sent its e-mail list of millions of supporters excerpts from two opinion articles praising Bush’s handling of the tape’s release on Friday and accusing Kerry of politicizing it.

In their final push, Bush and Kerry are shadowing each other around the same battlegrounds – Ohio, which Bush won in 2000 but has been tough for him now because of job losses; Florida, which could again be the decisive state in a razor-thin election; and the Great Lakes region, where Bush has put Kerry on the defensive in Iowa, Minnesota and Wisconsin – all won by Vice President Al Gore four years ago. Bush is also continuing to make strong runs in two Democratic strongholds, Michigan and Pennsylvania.

Although Bush aides are more optimistic than they were last weekend, the race is still so tight that he continued his relentless attacks on his opponent, naming Kerry a dozen times in a 41-minute speech.