When Mr. Paul’s campaign jet broke down last year in Wolfeboro, N.H., Mr. Romney’s wife, Ann, offered to let Mr. Paul, an aide and one of his granddaughters stay the night at their summer home on Lake Winnipesaukee. When Mr. Romney arrived later, he offered his jet to take them home to Texas. Mr. Paul, not wanting to impose, was grateful but declined both offers. In a Republican presidential contest known for its angry rivalries, the Romney-Paul relationship stands out for its behind-the-scenes civility. It is a friendship that, by Mr. Paul’s telling, Mr. Romney has worked to cultivate. The question is whether it is also one that could pay dividends for Mr. Romney as he faces yet more setbacks in his struggle to capture the 1,144 delegates needed to win the nomination.