From the top...
SENATOR McCain will have difficulty winning the election if he indeed is the nominee because he is a SENATOR.
The last Senator (or former Senator) who won an election against a non-Senator was Truman, who obviously had the power of the incumbency behind him, in the infamous "Dewey Wins" election.
Before that, you need to look at Warren G Harding in 1920 for a sucessful run for POTUS by a Senator or former Senator.
The reason McCain matches up well against Hillary is that... drumroll please... SHE'S A SENATOR!!!!
The raw data from the last 100 years:
* * *
Harding - Senate to POTUS, 1920
Truman - Senate to VP, POTUS via death, last POTUS to win vs non-senator Dewey in 1952.
Kennedy - Senate to POTUS, 1960 (ran against Senator Nixon)
Johnson - Senate to VP, POTUS via death, (beat Senator Goldwater in re-election)
Nixon - Senate to VP to unemployment to POTUS, 1968 (lost to Sen Kennedy, beat Senators HHH and McGovern in elections)
I agree, I don't like voting for Washington insiders who have already done enough damage to the country. I will hold my nose and probably vote for Rudy.
Correction: Kennedy ran against Vice President Nixon.
A senator seeking higher office might find his paper trail to be a major impediment to his aspirations. Opponents can point out, for example, when he voted for something before he voted against it.