Before folks launch into this please think!
For those living in New York City and elsewhere around the world - all politics are local and who replaces Saint Pete will be decided locally. What follows is a quick and dirty summary of the situation as it sits today in the wonderful land of enchantment.
The Republican bench in New Mexico is weak - their candidate for Senate will either be Heather Wilson or Steve Pearce. The Republican establishment fears nominating Steve Pearce because he is such a right wing wacko. This is another reason why Saint Pete's announcement is such a surprise - he knows that the Republicans in NM like Steve better than Heather but Steve is poison and Pete knows it. I always thought Pete would not run and in the end find another way to handle handing the nomination to Heather - maybe Pearce has agreed not to run, who knows - but its clear that something is bad wrong with Pete for him to make the announcement this early.
The Republican power structure (Pete leads it!) will do all it can to nominate Heather and my guess is that in the end they will succeed.
So unless we are really lucky the race is against Heather Wilson - she's smart and evil.
Please understand that NM is divided into 3 Congressional Districts - for simplicity call them Northern NM (NNM), Southern NM (SNM), and Albuquerque (Abq). NNM is the most liberal/progressive part of the State. SNM makes Texas look moderate to liberal. Udall does well in NNM but he won't win in Albuquerque (Heather's base) and he will loose horribly in SNM.
The only way he can win is if he runs against Steve Pearce. If the race is against Heather Wilson she will loose in NNM, win slightly in Abq and win big in SNM - ergo Heather wins.
The question that needs to be asked is - can Udall win big enough in NNM to make up for the huge loss he will face in SNM and a slight loss in Abq? Tom knows that and so does everybody else so he won't run.