I did an old soc.history.what-if post on this subject:
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I have recently been reading Elbert B. Smith, *The Presidencies of
Zachary Taylor and Millard Fillmore* (Lawrence: University Press of
Kansas 1988) and he makes some interesting points against the commonly
held belief that Taylor opposed the Compromise of 1850 and would have
vetoed it if he had lived. Smith suggests that there was really much
less difference here between Taylor and Fillmore than is often held.
When people say Taylor opposed the Compromise, they mean that he opposed
the Clay "Omnibus"--an attempt to address all the sectional issues in one
law. To Taylor, this was an improper attempt to combine unrelated matters
in order to use California as a bargaining chip for the ambitions of
Texas against New Mexico. But the Omnibus was never going to pass,
anyway, regardless of whether Taylor supported it. (Incidentally, even
Clay did not like the "Omnibus" concept--he came out for a combination
bill only after being pressured to do so by Foote and other Southerners.)
And--the crucial point--Taylor's opposition to the Omnibus does *not*
necessarily mean he would have vetoed the component parts of the
Compromise, presented as individual bills for his signature. In fact,
Taylor had often restated the standard Whig principle that the veto power
should only be used in exceptional cases--e.g., unconstitutional or hasty
and ill-considered legislation. Smith argues (p. 146-7):
"Both strong evidence and logic, therefore, indicate that Taylor would
have approved every part of the compromise in the form it ultimately
assumed when passed. The admission of California to immediate statehood
was Taylor's own idea. His policy toward New Mexico was a means to an
end rather than an end in itself. The final grant of self-determination
on slavery to a viable New Mexican territory with its populated areas
intact would certainly have satisfied him. He might have disliked the
financial reward given Texas for ceding most of its New Mexican claim,
but the measure was certainly constitutional, and a veto of it would have
contradicted everything he had said about the veto principle. A
slaveholder could not have objected seriously to a new fugitive-slave
act, and nothing he ever did or said indicates any objection to moving
the [DC] slave markets across the Potomac River into Virginia."
Of course, saying that Taylor would not have vetoed the Compromise does
not necessarily mean that it would have passed in the first place had he
still been president. Positive aid, not just a willingness not to veto,
was if not absolutely necessary, at least helpful, and here Fillmore was
certainly more useful than Taylor could have been. As Smith notes,
Fillmore, having served as Congressman and Vice-President, was better
acquainted personally with members of Congress, was more tactful,
understood the workings of the system better, etc. The mere fact that he
was known as an enemy of Seward's made some Southerners more friendly to
the compromise, and he apparently did use personal relations and make a
few patronage promises when the compromise was in its final stages. But
Smith thinks that by then pro-compromise sentiment was so strong in most
states (South Carolina of course being an exception) that passage was
practically assured.
BTW, Smith also suggests that had Taylor lived and presided over a
Compromise he would have been renominated and probably re-elected--and as a
slaveholder who did not believe slavery needed to expand, he would
definitely have opposed the repeal of the Missouri Compromise. (I agree
that he could have been renominated--even Fillmore almost was, despite his
reluctance to seek renomination. I am more dubious about his re-election;
this requires that he carry most of the South plus all the Northern states
that Scott carried in OTL and a couple where he came close.)
https://groups.google.com/d/msg/soc.history.what-if/BMyk87mPqlI/IRTPhI-M3fsJ
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I should add that Michael Holt (in *The Rise and Fall of the American Whig Party* puts more emphasis than Smith on Fillmore's role in getting the Compromise passed. The key vote, according to Holt, was the passage of the so-called "Little Omnibus" by 107-99. (Some of the preliminary votes were even closer.) Critical for its passage was the support of a number of Northern Whigs who had previously opposed any organization of new territories without the Wilmot Proviso. Holt thinks that while they may have been seriously worried about saving the Union, they were also influenced by the use of patronage by Fillmore and his Secretary of State, Webster.
https://groups.google.com/d/msg/soc.history.what-if/BL30IC12Og8/T6LSMI8bzVcJ Holt's analysis can be found on pp. 539-543 of *The Rise and Fall of the American Whig Party.*
http://books.google.com/books?id=5aGyVFn3VnMC&pg=PA539