Rudy Giuliani's national favorability before he ran for president was comparable to Hillary Clinton's today:
Though obviously, that didn't survive his presidential campaign. And he was never nearly as popular as a potential president within the GOP as HRC is within the Democratic Party.
Also, McCain's favorability in August 2004, ~4 years before the '08 election:
favorable 55%
unfavorable 19%
http://www.gallup.com/poll/1618/favorability-people-news.aspx#4Though again, that was because, at that time, he had enormous crossover appeal with Democrats and Independents. Less so within his own party.