I noticed Byron York's list of historical hurdles to McCain included this nugget:
The difficulty of succeeding a two-term president of one’s own party — a feat accomplished only once since Truman succeeded FDR.
While such a feat is rare in recent decades, a wider view of American political history is not completely barren of examples besides Truman-FDR and Bush-Reagan. Rutherford B. Hayes succeeded the two Republican terms of Ulysses S. Grant back in the 1870s.
If you want to argue further, Taft succeeded Roosevelt in 1912 after TR had completed almost a full two terms as a Republican (rounding out the second term of McKinley, who was also a Republican, post-assassination). Hoover succeeded Coolidge in a similar vein in the 1920s.
There's also the period of Jefferson through James Monroe in which the Democratic-Republicans had multiple successive two-term presidents (Jefferson-Madison-Monroe, followed by the single term of John Quincy Adams).
Shortly thereafter, Jackson's two terms as a Democrat were also followed by Martin Van Buren's term as a Democrat.
So, viewed from a higher height, I don't think the burden of succeeding a two-term president of the same party is quite as difficult as York paints it, although it is less common in the modern era.