George W Bush and John Kerry are going back to domestic issues as the US election campaign enters a key week.
Actor Michael J Fox added support to Mr Kerry's apparent comeback
The two men will hold another debate and the vice-presidential candidates will also meet for a TV contest that is more keenly anticipated than most.
Correspondents say Mr Kerry has been on a high amid a widespread feeling that he won the first debate - on foreign and security issues - with Mr Bush.
Opinion polls support that, and indicate Mr Kerry is bouncing back.
A survey published on Monday found that Mr Bush and Mr Kerry were tied with 49% support each among 772 likely voters questioned - a comeback for Mr Kerry who had been eight percentage points behind before last Thursday's nationally televised debate.
Among all registered voters, the USA Today/CNN/Gallup poll had Mr Bush in the lead by two percentage points - giving him 49% and Mr Kerry 47%.
The findings echo those of a Newsweek poll published at the weekend that also had Mr Kerry regaining support after the first presidential debate, which was watched by more than 60 million Americans.
Correspondents say the results - reversing a slight lead for Mr Bush - suggest some voters have changed their preference after the debate.
On Monday, both candidates returned to domestic issues that are set to be at the heart of much of their second debate to be held at the end of this week.
Mr Bush signed legislation to extend tax relief for middle-class families as well as incentives for businesses, saying the law "comes at just the right time for America".
"Unless we acted, a family of four earning $40,000 would have seen their federal income taxes rise by more than $900," he said.
"That would have been a burden for hardworking families across America. And it would have been a setback for our economy."
He held the ceremony in Des Moines in Iowa - a key battleground in this year's election and one that he lost narrowly in 2000.
Mr Kerry was in New Hampshire - another swing state - where he concentrated on health issues, restating his pledge to expand federal support for stem cell research.
"The hard truth is that when it comes to stem cell research, our president is sacrificing science for ideology and playing politics with people who need cures," Mr Kerry said.
He was supported by actor Michael J Fox, who suffers from Parkinson's - one of the diseases that some believe may be treated or cured one day if scientists can discover how to use stem cells to replace lost or damaged cells.
The Bush campaign insists there is no White House ban on stem cell research, but opponents say that the limited amounts of funding and stem cells made available to researchers mean useful scientific work cannot be carried out.
"It's kind of like giving us a car and no gas and [Mr Bush] congratulating himself for giving us a car," Mr Fox said.
Elsewhere, the two main running mates are preparing for their only head-to-head contest of the campaign.
The BBC's Justin Webb in Washington say the Democrats are hoping their vice-presidential candidate, John Edwards, will add to Mr Kerry's momentum if he can win his debate with Republican counterpart Dick Cheney on Tuesday.
The debate spotlight will switch to Mr Cheney and his challenger
Observers say the new closeness of the race adds to the interest in the verbal battle between Mr Cheney, 63, and the youthful-looking Mr Edwards, 51.
While Mr Cheney is portrayed as the Bush campaign's attack dog, Mr Edwards is seen as a man who brought an obvious charm and charisma to the Kerry camp, which had been portrayed as dour.