Bush: Yes, on immigration.
Cruz: Yes, book deal disclosed by his agent in April.
Jindal: Not since before 2012 election.
Paul: No, not since just before the 2012 election.
Perry: Not since before 2012 election.
Rubio: Yes, coming in late 2014 from the publisher of his 2012 memoir.
Santorum: Yes, "Blue Collar Conservatives" released in late April, says: "Do Republicans really care less about the person at the bottom of the ladder than Democrats do? To be painfully honest, I would have to say in some ways 'yes.'"
Ryan: Yes, coming in 2014.
Walker: Yes, out in fall 2013.
GO TO IOWA: Its caucuses are the opening act of the nomination contest.
Biden: Yes, spoke at Sen. Tom Harkin's fall 2013 steak-fry fundraiser, a must-stop for many Democrats seeking to compete in the leadoff caucuses. Then in May, attended party for Iowans who came to Washington for annual lobbying trip. Raised money for Iowa congressional candidate Jim Mowrer. Schmoozed with Iowa power brokers during 2013 inauguration week in Washington.
Clinton: No, avoiding big primary/caucus states. But Ready for Hillary is mobilizing for her in the state.
O'Malley: Yes, headlined Harkin's 2012 fundraiser.
Bush: Yes, in 2012.
Christie: Yes, in 2012. More travel driven by politics in the cards now that he's chairman of Republican Governors Association for 2014 election year.
Cruz: Yes, four visits in eight months.
Jindal: Yes, summer 2013 visit, then flew with Iowa governor to governors association meeting in Milwaukee. In Iowa seven times in 2012.
Paul: Yes, three times in 2013. In March, snagged the state GOP chairman, who announced he was quitting to join Paul as an adviser.
Perry: Yes, third trip since November coming up: He's to campaign for Gov. Terry Branstad in late spring. Visited Des Moines suburbs and Davenport in February, meeting GOP activists and attending an event with business leaders sponsored by Koch brothers' Americans for Prosperity. Met Branstad and addressed Des Moines crowd of 400 in November.