Republican Rick Santorum ends second bid for president
Republican Rick Santorum has dropped his bid for US president and backed Florida Senator Marco Rubio instead.
The former Pennsylvania senator won the Iowa caucus in 2012, but finished bottom in Monday's vote in the state.
He described Mr Rubio, who finished third in Iowa, as a "born leader" with an "optimistic" outlook he admired.
Iowa was first in the state-by-state contest to pick presidential nominees, with voters in New Hampshire getting their turn next Tuesday.
Mr Santorum is known for his hardline conservative views on gay marriage, climate change, US acceptance of refugees and abortion.
The Christian conservative campaigned on a message of strengthening the middle class and preserving "traditional family structures".
He was largely relegated to the "undercard" portion of the Republican debates and complained about his lack of media attention.
The Republican field is now down to nine from the original 17.
Republican Rand Paul, who represents the libertarian wing of the party, dropped out on Wednesday as well.
Former Arkansas governor Mike Huckabee dropped out shortly after Ted Cruz won the Iowa caucus.