It's 2011. Why don't conservative Republicans (all) join the Tea Party and form a new political party in the United States or join the American Conservative Party?

There is no need to form a new Party even if it could be done.  The Republican Party has a long, established history, office space in Washington and in every state and large county, a large paid staff and a great brand that has 100% name id.  The Tea Party was formed because voters had lost all confidence in the Republican Party's ability to adhere to its advertised principles.  While it's true that the Republican administration and Congress failed to rein in spending, it doesn't follow that there was a failure of Republican ideas.  The Tea Party movement eventually voted for the Republican Party candidates in almost all cases.  While they don't see moderate Republicans as their best friends, they do see them as allies, because almost all intelligent politicians would rather form a coalition of voters who generally have the same goals than to be a pure, unadulterated permanent 30% minority.

The short answer is that would guarantee losses of major proportions for both the new TP and the existing GOP. That said, I think our country would greatly benefit from having 6 or more parties - maybe 10 or 20. The founders did not want political parties. They would roll over in their graves at the thought of paid consultants (sorry, Gary, but they would)... Our system of government was designed to work for the interests of the people - without the people splitting into 2 groups. This has been corrupted - possibly beyond repair. It's a sad thing - maybe the next generations will fix it by amending the Constitution.

Republicans voters generally back Republican candidates. Just like Democratic voters generally back Democratic candidates. Splitting off and forming a third party means you automatically forgo many of those votes you automatically received from people who generally backed what you back and thus vote straight party ticket. Thus all you end up doing is splitting the vote on your side and handing opportunity to the opposing party. It's far easier to try to change a party internally, with one wing or another gaining dominance, than to build a whole new political party that then is going to be running against the very same people who once were nominal allies.

Well, I'd like to say that the Tea Party was hi-jacked by republicans, changing it from a fiscal movement that people from both parties supported, to a movement of republicans that had a significant social agenda along with changes to it's fiscal movement. I know because i was a Tea Party supporter until a year ago when the change became obvious, Tea Party members started asking for abortion to be illegal, that defense spending to not be cut, for social security and medicare to be ignored and for all other forms of welfare to be removed from government. Frankly, since the Tea Party was hijacked, I noticed those changes and it's frankly made me turn my back from something that I thought was good for the country. It doesn't need to be a party, just a movement of the general populous from either or neither party about what concerns them.

One, Because the TEA party, as a cause, is one dimensional. Kind of like making the NRA a new party. Two, Because there is an American Conservative Party already.  See http://www.Amconparty.com

It's not logical or wise in any way. Only a fool would believe that splitting off into a fringe or offshoot party (in this century) is the best way to move any of their agenda items forward. Both a moderate or hardcore conservative will have a better chance of affecting change by changing the Republican party from within than by creating or joining a third party. For example, I would like to see Republicans get on board with same sex marriage and stop opposing it. My choices are to either persuade and organize other like-minded Republicans to further persuade other like-minded Republicans we need to make the change within the Republican party, or I can get some of those like-minded Republicans to join the new party I'm creating that'll have a platform very similar to Republicans except for a few planks. Keep in mind, both parties agree on 90% of the issues. Elections come. Each party nominates someone. You have a Republican party candidate, a New Republican Party Candidate, and a Democrat Party candidate. Republicans get 43% of the vote, the SSM Republicans get 10% of the votes, and the Democrats get 47% of the votes. The Democrats win. The SSM favoring republicans sort of win too on the one issue, but they lose on the other 90% of their issues. The Tea Party is not a separate party. They are doing exactly what I've recommended. They've organized to attempt to steer the party in a direction they like. Judging by how obsessed the Democrats are with complaining about them, they're doing it very effectively.

Why don't liberal Democrats all join the Socialist Party and form a new political party? Answer that question, and you will have answered your own question.