Ron Paul’s rallies this year have yielded quirky and eclectic crowds — bow-tie-wearing libertarians, scruffy anti-establishment types, large religious families and packs of antiwar college students, all drawn with an unusual fervor to the presidential candidate’s unique libertarian message.

Many mainstream Republicans have long viewed his supporters as a fringe element. But they face a gnawing question: What if Paul’s followers do not fall in line behind the eventual GOP nominee, who will need every vote possible to defeat President Obama in the fall?