Don't be so sure. He'll be out of the race long before he has to worry about his House reelection bid. His spokesman even said this "wouldn't affect" his next House campaign. I think even he knows he can't win it.
Probably just wants to inject his one issue into the discourse.
Since Rep. Hunter and Rep. Paul aren't resigning their House seats to run for the presidency, Rep. Tancredo should not be expected to resign his seat.