Rush Limbaugh is ailing. And so is the conservative talk-radio industry.

Rush Limbaugh, the most successful talk-radio host in history, is ailing. And so is the medium he helped revolutionize over the past 30 years.

Faced with aging and shrinking audiences, competition from newer technologies and financial problems for the biggest station owners, talk radio is in decline — both as a business and a political force. Once a leading platform for popularizing conservative candidates and policies, talk radio is on the verge of becoming background noise, drowned out by a cacophony of voices on podcasts, cable TV and social media.