They have dropped off the campaign trail and dispatched their running mates to court voters in battleground states.
The debate, which focuses on international affairs, will be the final chance for each to lay out his policy platforms and engage in verbal jousting in front of tens of millions of TV viewers just 15 days before voters head to the polls.
With both sides conceding that the race to November 6 will go down to the wire, and amid a consensus that each candidate won one of the previous two debates, the stakes for Monday's clash are enormous.
And just as they study up on the particulars of US policy about the Middle East, China and Russia, the New York Times reported a possible breakthrough on talks with Iran – a report quickly squelched by the White House.
Citing unnamed administration officials, the Times reported that Iranian officials had agreed to direct US-Iran talks over Tehran's nuclear program, after years of secret talks between the two sides.
The Iranians insisted that such negotiations wait until after the US election, when they will know who the next president will be, the report said.
The White House swiftly denied any deal had been reached, saying it was still working on a "diplomatic solution."
"It's not true that the United States and Iran have agreed to one-on-one talks or any meeting after the American elections," National Security Council spokesperson Tommy Vietor said in a statement.
The Times story broke just as the two US candidates were hunkered down for debate prep.
Obama was gathering his team at Camp David, the remote presidential retreat in Maryland's Catoctin Mountains, while Romney opted for a bit of sun, heading to a beach-side resort in debate site Boca Raton, Florida, where he is huddling with top strategists.
The challenger also took the opportunity to hit up wealthy donors one last time. Romney attended his final fundraising event of the campaign Saturday in Palm Beach, an aide said.
Obama attended his final fundraiser earlier this month.
Epicentre of the epicentre
With the candidates off the trail, it was up to their deputies to sway voters.
Vice-president Joe Biden was in Orlando, Florida, where he ducked into a campaign field office to energise volunteers before heading to an event in St. Augustine.
"We wanted to come to the epicentre of the epicentre," Biden said, mindful that the Orlando-Tampa corridor is the most vital region of the largest swing state of all.
"You guys produce, we win Florida," Biden said. "We win Florida, this is all history, man."
The Republican ticket is placing a similar premium on the Sunshine State. Romney and running mate Paul Ryan shared the stage Friday at a rally in Daytona Beach.
Then Ryan went on a multi-state tour Saturday, from key battleground Florida to Pennsylvania, a state that had been seen as a sure bet for Obama but where Romney has made recent inroads, then Ohio and finally on to Nebraska.
Ryan, chairperson of the House Budget Committee and creator of a controversial budget plan that envisions dramatic cuts to federal spending, told a crowd in Pennsylvania's Moon Township that America could no longer endure an outsized government.
"Look, the choice is this: Do we limit the size of our government, or do we limit the growth of our economy?" he said.
"Mitt Romney and I believe we need to limit government so our economy can grow."
Obama has caught flak from Republicans – as well as from Democrats driven to near-panic over the president's polls slide in recent weeks – for not articulating a clear vision for the next four years.
For their part, Obama supporters attack Romney for not revealing details of which loopholes or deductions he would close or end in order to pay for his planned 20% tax cut.
Just over two weeks remain and polls show the candidates neck and neck, with battlegrounds Florida, Ohio and Virginia proving crucial.
With the election boiling down to a handful of key states, both parties are hopscotching across the battlegrounds.
Obama's team announced that the president will launch a two-day blitz beginning Wednesday to six states – Iowa, Colorado, Nevada, Florida, Virginia, and then Illinois, where he casts his early ballot in hometown Chicago.
Romney too will be visiting Colorado, Nevada and Ohio next week. – Sapa-AFP