Mitt Romney is hoping to change the trajectory of his campaign as he and president Barack Obama study for their first debate on Wednesday.
It will be one of Mr Romney's best, and last, opportunities to stop Mr Obama's rise in the polls.
Adding to the performance pressure was the growing momentum in early voting, with the most important of the battleground states that will decide the November 6 election, Ohio, already starting to take ballots.
Mr Obama was with top advisers at a desert resort in Nevada. Mr Romney was practicing in Massachusetts before heading to Colorado, the site of the debate and another of the handful of states that will determine the election.
Polls show Mr Romney trailing Mr Obama in many of those nine battleground states, which do not reliably vote Democrat or Republican and have been deluged by campaign ads and visits. All but two of them have early voting.
The first of the three presidential debates is focused on domestic issues like the economy, which remains voters' top concern. Mr Romney has a chance to convince the public that he is the better candidate to turn the country's high unemployment around.
"What I'm most concerned about is having a serious discussion about what we need to do to keep the country growing and restore security to hardworking Americans," Mr Obama said during a rally in Las Vegas. "That is what people are going to be listening for. That's the debate you deserve."
Republicans were keeping up the pressure on Mr Obama on international issues, namely his administration's handling of the attack on a US consulate in Libya that led to the death of the US ambassador and three others.
The Obama administration has called it a terrorist attack. It came amid violent protests in the Muslim world over an amateur anti-Islam film made in the US
Mr Romney, in an opinion piece in The Wall Street Journal, repeated his criticism of Mr Obama for having called the attack and other unrest in the Middle East "bumps in the road."
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