You're right, though Pat's been gone from the party long enough that no one should associate him with Republicans.
The problem is not so much Pat himself, but the fact that the existence of nutbags like Pat serves to perpetuate the paranoia of Jewish voters who remember, or whose parents remember, a time when Pat-type thinking was a pretty big part of the Republican party.
Pat is like the Archetypal devil for people who lived through a really difficult time, when national leaders like Henry Ford or Charles Lindbergh were openly sympathetic to the Nazi party and willing to say that the Jews were trying to get America into an unneeded war with a fine man like Hitler for commercial or financial reasons. Its probably no coincidence that the mainstream media has made Buchanan and Novak into the ideal "Republicans" for the public to see, when in fact neither of them actually is.
I mean by the same token of letting the fringe scare one away from the mainstream, the reason I don't vote for Democrats is that I believe that they have not really come to terms with the evils of Socialism. Likewise, there is a big part of the left in the US who are pretty reasonable on many issues, but who think that the Republicans still harbor sympathies with the Birchers and America Firsters. And in fact to whatever extent that (in my opinion) ugly segment of American politics does exist it probably is basically Republican.
Buchanan's roots go right to Father Coughlin. Political parties exist on a spectrum, and the spectrum of the Republican party is more likely to include Buchananite logic that the Democrats are.