I'm with you in being surprised at the claim that INS people aren't Civil Service and effectively immune.
But the Travel Office is not a good example. The scandal of the firing of Billy Dale et. al. was not the fact that they were dismissed; these people worked in the WH rather than civil service and served at the pleasure . . . (what a thought!).
The TO crew was pounced upon, evicted, and (in the case of Billy Dale) criminally charged. This was done at the behest, apparently, of Hillary. Billy Dale had in fact cut corners in order to accomplish his mission expeditiously, allowing the appearance of impropriety to occur. But the fact apparently was quite contrary to that appearance, and the jury didn't buy it at all.
Not only so, but journalists were the actual clientele of the TO, they actually paid the money that Billy Dale handled for their convenience under the president's orders (I believe it was JFK who created the WH TO to curry favor with journalists). And the journalists were satisfied customers who didn't buy the brief against Dale, either. Why then did Hillary do it so brutally? She thought it was better politics that just exercising arbitrary authority!! Abusing the FBI, that she thought was fine, but firing someone 'cause you felt like it was a no-no . . .