By Steve Holland and Andy Sullivan NATIONAL HARBOR, Md. (Reuters) - Republican Jeb Bush asked skeptical conservatives to consider him a “second choice” on Friday but refused to back down from policy positions that have led many right-leaning activists to view his potential presidential candidacy with suspicion. "I'm a practicing, reform-minded conservative," the 62-year-old former Florida governor told the Conservative Political Action Conference (CPAC) in Maryland near Washington. Many attending the annual gathering of grassroots activists made clear they prefer a potential Bush rival, Wisconsin Governor Scott Walker, among others. Bush was heckled and booed, but the antipathy was balanced out by enthusiastic supporters who showed up shortly before he spoke and clapped heartily and aggressively.