Here is the problem for the Republicans as I see it. They have within their ranks, and particularly in the house, a fraction of their party that is quite far from the centrist thinking of something close to 60-70% of the electorate. These representatives come from safe districts, so politically their concern is less with centrist America and more with their particular constituents -- that's politics! From a purely practical standpoint, however, the Senate Republicans, who have to answer to a much broader electorate, recognize that their electorate is more centrist than the narrowly focused fraction of their party in the House.
These Senators realize that with a Democrat in the White House, and a minority in the Senate, there is no possibility of their getting their way by shutting down the government or causing a default. They know that they are playing with political fire, and they have nothing to gain politically by throwing their lot in with the House Republicans. They are between a rock and a hard place, and trying to salvage their political careers.
The fundamental problem for the Tea Party is that they are out of step with the majority of Americans. They may be right, they may be wrong, but until they can build a consensus among the broader electorate they will be forced to remain a vocal sideshow.
