Endangered Newt enhances comeback with shock primary victory

The win marks a dramatic turnaround from Mr Gingrich’s earlier poor showing in the first two contests of the party’s presidential race.

It sets up the likelihood that the contest, which Mr Romney once seemed poised to wrap up quickly, could drag on for months.

It also puts Mr Gingrich in a position to establish himself as the true conservative alternative to Mr Romney, who some Republicans see as too moderate.

Mr Romney has benefited by having the conservative vote divided among Mr Gingrich, former senator Rick Santorum and Texas governor Rick Perry, who dropped out on Thursday.

An exit poll conducted for The Associated Press and US television networks showed Mr Santorum and congressman Ron Paul were far behind.

Mr Gingrich led by a wide margin among the state’s heavy population of conservatives, born-again Christians and supporters of the small-government tea party movement.

Mr Gingrich also won the support of voters who said they cared most about picking a candidate who could defeat Mr Obama. Mr Romney has made the claim that he is the most electable candidate a key part of his campaign.

In another development, Gabrielle Giffords of Arizona says on her Facebook page she intends to resign from US Congress this week to concentrate on recovering from wounds suffered in an assassination attempt a little more than a year ago.

According to officials in Washington, her resignation is expected to take effect today.