Assorted responses:
Thompson is good on most issues, bad on illegal immigration. He would be a very viable candidate.
Paul is good on most everything, bad on the war with militant Islam. (Refresh me again as to his position on illegal immigration?)
I was a GDI until the 2000 Republican primary, where I registered so I could vote for Keyes. After 2, Keyes has been a...disappointment.
Tancredo's message of enforcing our immigration laws has been polled over the years and is wildly popular. Not just a little popular, but deck-clearingly, "huge majorities of Republicans & Independents and an honest majority of Democrats" popular. Jack Kemp and like-thinkers are the minority in the Rep party, Dem party, and the unaffiliated. There are a few problems with riding the pro-enforcement message home to victory:
1. It is one issue of many & informed folks balance a number of issues before voting.
2. Politicians who get elected swim in a sea populated by those who favor LOTS of illegal immigration (gov't employees, journalists, academics, etc)
3. Many business donors don't want to trade off the deal they have: concentrated benefits and socialized (dispersed) costs.