The four remaining U.S. Republican presidential candidates have held their last debate before next week's crucial Florida primary, sparring over immigration, tax records, and a proposed moon colony, in the state that hosts much of the nation's space industry.

Frontrunners Newt Gingrich and Mitt Romney traded barbs Thursday at the debate in Jacksonville, in northern Florida. The closest U.S. state to Cuba, Florida is home to a large Cuban immigrant community.

Accused by Gingrich of being the anti-immigrant candidate, Romney called the remark “repulsive” and demanded an apology. Gingrich accused Romney of wanting to force all illegal immigrants, including the elderly, to leave the country. Romney said he wants people to come to the United States legally and work.

Romney attacked Gingrich's recently announced proposal to establish a colony on the moon, saying he would rather see the money put toward rebuilding housing in the United States. Contender Ron Paul quipped that, instead of establishing a colony, perhaps “some politicians” should be sent to the moon instead.

As Florida also has a large Jewish population, Israel was a key factor in the debate. Both Romney and Santorum said there can be no peace in the Middle East until Palestinian leaders recognize Israel's right to exist. They both criticized President Barack Obama who has called on Israel to stop building Jewish settlements in lands that could be part of a future Palestinian state.

Whoever wins the populous southern state next Tuesday will pick up lots of delegates to the national convention, and could take a firm lead in the Republican presidential race. Unlike years past, in 2012 no clear leader has emerged after three previous state contests.

Meanwhile, U.S. President Barack Obama is on a five-state tour, both to shore up re-election support and to sell his new economic plan. On Friday he visits Ann Arbor, Michigan, to talk about using education as a way to boost the economy and create jobs. Later in the day he will travel to the state of Maryland to attend a Democratic issues conference.