Rudy Giuliani's presidential candidacy is the best thing that will happen for the Democratic candidates this year. He's going to lose. Yes, I know he's the Republican frontrunner in some polls, but Howard Dean was the frontrunner for a while in the last contested presidential primary season.
On his way to losing, Giuliani is going to divert a lot of money away from the inevitable Republican nominee, John McCain. Giuliani's losing campaign is also going to pull a lot of pro-choice, independent voters away from McCain in the general election. McCain has had very strong appeal among those voters for years because, among other things, they don't quite realize how hard-core his anti-abortion position actually is. When Republican primary voters discover how liberal Giuliani has been on social issues--along with how many wives he's had and how many gay men he has lived with while waiting for a divorce to come through--they are going to abandon him faster than Democratic voters fled from Howard Dean. But the only way they are going to "discover" Giuliani's record on social issues is for John McCain to tell them about it. McCain's campaign has the most vicious attackers in politics today, including Bush campaign graduates and the Swift Boat attack team. They are going to make Giuliani look very bad to conservative voters, but, in the process, they are going to make McCain look bad to moderates he will need in the general election.
The attacks on Giuliani are also going to make the Democratic nominee look better. Only the New York press (which includes the national press) thinks being The Mayor is adequate preparation for being president. McCain's attacks on Giuliani will include double underlining Giuliani's lack of experience in federal government. Giuliani's experience with the biggest items in the federal budget--Social Security, Medicare, and Defense--is nonexistent. The McCain campaign will do the Democrats the favor of showing that the current Republican frontrunner has less relevant governing experience than Senators Obama and Clinton, who will owe McCain a thank-you note.
No mayor of New York has been promoted by voters to higher office in my lifetime. Big city mayors don't play well with voters outside their city anymore. Just ask John Lindsay, Ed Koch, Kevin White, Tom Bradley, Dick Riordon. Rudy Giuliani is no exception.