Tuesday is the last full day the U.S. presidential candidates have to prepare for their first debate, which could be a crucial moment for Republican Mitt Romney.

The latest polls give President Barack Obama a significant lead over Mr. Romney in many of the so-called swing states that may decide the election. An impressive performance by Mr. Romney in Wednesday's debate could make it a much tighter race.

The campaign goes on even while the candidates are huddled with their advisers and practicing.

Mr. Romney criticized the president's foreign policy in an opinion piece in Monday's Wall Street Journal. He wrote that under President Obama, the United States is at the mercy of world events rather than shaping them. He said Mr. Obama believes weakness will win favors from America's adversaries.

An Obama spokesperson called the comments “reckless” and “irresponsible.”

Wednesday's debate at the University of Denver in Colorado will focus on domestic issues. The candidates will debate foreign policy on October 16 and 22.