This view of the American electoral system as inimical to third party politics is the result, I think, of an unfortunate over-emphasis on presidential politics. The Canadian parliament and the British House of Commons are both elected along very similar lines to the US House of Representatives (first past the post elections in small, single-member constituencies) and each feature five parties with representation in parliament.He has a point, and I think it's legitimate, although it does require legislators who don't have even an eye on the Oval Office, and parties that are willing to give up that possibility. Most politicians would want to join one of the big established parties simply because having the *possibility* of a presidential candidate being from your party is compelling, but the American system isn't nearly as party-centric as the Westminster one.
In those Westminster systems, however, there's no real point to electing MPs unless you stand a reasonable chance of electing a majority because it doesn't really matter what any individual member thinks. In the US, however, where we have two parties in pretty even balance and a politics of ad hoc coalition-building, minor parties with just a handful of representatives could make the difference on several key votes. Reps Flake and Paul really might be well-advised to leave the GOP, see if they could recruit a couple more like-minded backbenchers, form a small Libertarian caucus, and try to run candidates in a few more ideologically friendly districts. None of them would ever get elected president, but then again none of them are ever going to be elected president anyway.
(Actually, come to think of it, that may be the problem. American politicians already enjoy far more freedom than their counterparts elsewhere- that might mean that independent-minded legislators won't be so alienated as to leave. The anti-RINO and -Dino movements may change this, however.)