I disagree too. When actually faced with the choice of Hillary or Rudy. Conservatives will have no problem showing up and voting for Rudy. They may pine for a different Republican candidate, but the thought of Hillary and Bill back in the White House will launch all conservatives to the polls in significant numbers.
Still, the 2000 election was a squeaker. In 2004, the GOP received a decent victory margin (51% - 48%) and Bush became the first Presidential candidate since 1988 to receive a majority of the popular vote. In 2004, Bush increased his vote total to 62 million, an 11 million increase, while Kerry received 59.4 million of only 8.4 million. A fraction of that increase probably came from Nader supporters, as the long time consumer activist received only 400,000 votes in 2004, vs. 2.4 million four years earlier. Bush's improvement is largely attributed to evangelical voters supporting him. In 2000, Bush received 68% of the white evangelical vote, increasing to 78% in 2004. In both elections, white evangelicals represented 23% of the electorate. About 5.3 million more white evangelicals voted for Bush in 2004, representing almost half of the Bush increase that year.
Conversely, what hurt the 2006 GOP Congressional campaign was a falling away by both economic and social conservatives. Unfortunately, I don't believe fear of the Clintons will be sufficient to draw these conservatives to Giuliani. In 1996, Dole received almost the same number of votes that the elder Bush had in 1992 (39.2 million vs 39.1 million) in spite of four years of attempts to socialize medicine, permit open homosexuals in the military, mysterious deaths like that of Vince Foster, and gossip about Bill Clinton's sexual escapades. Additionally, some 11.5 million voters who had supported Perot in 1992 either voted for another candidate in 1996 or did not vote.
As for Hillary's lack of charm, remember that no one ever accused either Gore or Kerry of being personable or lovable, yet both men received almost half of the total national vote.
Even without a strong third party candidate, Giuliani will lose a portion of the conservative vote, especially white evangelicals and possibly church-going white Catholics as well. Gun owners and economic conservatives also have reason to be unenthusiastic about him. However, Giuliani may be able to offset the loss through breaking the lock the Democrats have had over the 11 Northeastern states and California. Picking up PA, NJ, NH, DE, and maybe ME and CT would make up for possible losses in the Upper South and the Border states. If he can turn California, as Schwarzenegger has with his brand of politics, away from the Democrats, he can win even if he loses OH, IA, and maybe NM.