Hillary Clinton has taken husband Bill on the campaign trail in Iowa
Democrat Hillary Clinton has been joined by husband and former president Bill for a three-day tour, while Barack Obama has taken his family to Iowa.
Also in the state for Independence Day are Democrats Joe Biden and Chris Dodd and Republican contender Mitt Romney.
Iowa is one of the first states to pick who will run for president for each party, making it a key campaign target.
Its early caucus gives it disproportionate influence over the presidential nomination process despite its relatively small size, with about 1.8 million voters.
With less than seven months to go before the primary and caucus season begins, candidates are keen to make an impression on what is a predominantly rural, small-town state.
Professor Cary Covington, a political scientist at the University of Iowa, said: "Iowa is the first state and so if you don't do well in Iowa, that puts you under a cloud for the whole way and makes it much harder to make progress in later states."
Mrs Clinton has been leading national polls but is trailing in Iowa to former North Carolina Senator John Edwards, who built up a strong base there when campaigning in the 2004 presidential race.
She maintains a lead over Barack Obama in the state but appears keen to regain ground lost to Mr Edwards.
Bill Clinton made his first major public appearance by her side at the Iowa State Fairgrounds in Des Moines on Monday, describing her as the candidate best qualified for the job.
The pair were due to campaign in Iowa City and Davenport on Tuesday and to take part in a 4 July parade in Clear Lake on Wednesday.
Mr Romney, former Governor of Massachusetts and a frontrunner in the Republican race, will also march in the Clear Lake parade.
He led fundraising for the Republicans in the first quarter, raising $20.6m and lending himself $2.35m.
Aides to former New York mayor Rudolph Giuliani said he had now more than $18m cash in hand and no debt.
Senator Obama, from Illinois, reported raising $31m for the primary battle on Monday, putting him ahead of Mrs Clinton with $21m for the primary and another $6m for the general election.
Mr Obama is expected to appear with his family at Independence Day events in Pella and Oskaloosa.
Former governor of Wisconsin and Republican candidate Tommy Thompson will be campaigning in the state later in the week.
Since Saturday, Republican candidates Tom Tancredo, Congressman for Colorado, former Arkansas Governor Mike Huckabee, Kansas Senator Sam Brownback, former Virginia Senator Jim Gilmore and Texas Congressman Ron Paul have all made stops in Iowa.
Mr Brownback, with 77 visits since January according to the Washington Post newspaper, is perhaps the state's most frequent caller among the presidential hopefuls.
But whether all the candidates' efforts in the state have paid off will not be known until Iowa holds its caucuses early next year.
"What is important in Iowa is to finish in the top two or three candidates," says Professor Covington."Iowa is how we tell who's a pretender to be a candidate and who's a serious possibility - and the people who finish down the lists are going to see media attention dry up and financial contributions go away, and they will shortly be out of the race."