The reason my prediction isn't just your-guess-is-as-good-as-mine prediction is explained well here:
Sanford Levinson, a constitutional expert at the University of Texas Law School in Austin, said it is extremely hard to amend the Constitution. If the ban on gay marriage passes the House and Senate, he said, opponents could stop it by getting the support of one house of the legislature in just 13 states."[O]ne house of the legislature in just 13 states"--think about it. That's the 3/4 supermajority requirement of Article V of the Constitution. It's no mean feat to get through Congress with an amendment either: Article V imposes a 2/3 supermajority requirement on both Houses of Congress.
Levinson said Bush's support was "a free pass" because he probably knows how difficult it would be to get through Congress, let alone through 38 states.
"The idea is for Bush to throw red meat to the Republican right, secure in the knowledge that this is not going to go anywhere," he said. "If it did go anywhere, it would tear the Republican Party apart."
So even if a large majority of Americans love the idea of adding this blot to the Constitution--and I don't think they will--it still won't happen, because it is just too hard to amend the Constitution. Things might be done with statutes or state constitutions, but the U.S. Constitution is different. It just won't happen. So people on all sides of this debate need to think clearly about what they mean to achieve through this exercise. Personally, I think it is a shame that this hot debate is becoming so prominent during the Presidential election year, because it detracts attention from the issues that have much more to do with the Presidency, such as the war against terrorism.