Republican presidential candidate Mitt Romney has got his campaign back on track by winning the Maine caucuses, holding off a strong challenge from the outsider, Texas Congressman Ron Paul.

Although Romney will be relieved to have chalked up a victory after losing three contests in mid-week, he saw a huge 31% majority from the 2008 Republican nominating race shrink to just 3%. The narrowness of the win keeps alive doubts about his ability to excite the conservative base, and concerns that a lack of enthusiasm could prove a problem against Barack Obama in November.

Romney now has four wins (New Hampshire, Florida, Nevada and Maine) to Rick Santorum's three (Minnesota, Iowa and Colorado), plus Santorum's victory in a popularity contest in Missouri where nothing was at stake. Former House Speaker Newt Gingrich has just one, South Carolina.

Maine was a big disappointment for Paul who invested a lot of time and had hoped finally to make a breakthrough and win a state.

With 95% of the votes counted – some caucuses had to be delayed by snow – Romney took 39%, 2,190 votes, to Paul's 36% with 1,996 votes. Santorum took 18% and Gingrich 6%. Neither Santorum or Gingrich campaigned in Maine.