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Do you have any reason to believe that they will annul the election?"
I would say it is highly unlikely given the way their proceedings have gone thus far. We have not seen the Electoral Tribunal undertaking the kind of investigation before the public which says that they might annul the election. Of course; that does not mean that they might not be doing exactly that in private.
Just to give you a complete answer to your question, I'm going to translate one paragraph from
an El Universal article up today entitled "The Process, Hours from the Result," which summarizes the arguments that have been made to annul the election:
. . . Moreover, it is argued that the lack of certainty in the Program of Preliminary Electoral Results, the growth in the number of null votes in relation to the election of 2000, the slowness of the IFE to face and order the suspension of the defamatory [television and radio] spots, the supposed use of social programs in favor of Felipe Calderon, the speech of the Managing Director [of the IFE] Luis Carlos Ugalde that he had confirmed the advantage of the PAN candidate in the voting, excessive spending in the media, the meddling of the ex-Spanish President Jose Maria Aznar and the lack of control over the spending of presidential aspirants, before the elections. . . .
Note: If you're wondering about the Aznar "meddling issue" click here.
That is the sum total of arguments. I seriously doubt anything will come of the whole group of them taken together, but there is just something about judges that bothers me, even when I think they're doing their job.
And by the way, I would rate Calderon's chances at winning a second round as almost a slam dunk. Robert Madrazo of the PRI knows he doesn't have a chance and I cannot envision the PRI campaigning for the position with any fervor. I would expect them either to endorse Calderon or just stay out of his way. So that wouldn't be the worst outcome.
One more thing; AMLO himself has said that he thinks that the tribunal's declaration of Calderon as the winner is all but a "done deal," so that pretty much tells you what to expect.