A far more accurate comparison would be the Tea Party. And those on the left who enjoy watching the Tea Party destroy the Republican Party REALLY need to learn from what happened in Canada:
Canada's Tea Party movement started as the Reform movement within the Conservative Party. Their discontent with the Conservative government came from what they saw as a lack of power for the far right within the party. Runaway deficit spending which the Conservative party promised to stop but instead accelerated. A lack of democratic reforms. And other claims that those watching the Tea Party would find familiar. In 1987 they split off to become the "Reform Party."
Early on the Reform Party was marked by wingnuttyness and racism. It was home to the religious right. Sound familiar?
But it's extremists who get all the press. Dumb statements and policies are news; reasonable ones aren't. Because they split the conservative vote, the old Conservative party was reduced to almost no seats in the next election. Some of the far right even celebrated the destruction of the moderate right.
And so most remaining Conservative candidates went over to the Reform Party.
The old conservative party (The Progressive Conservative Party of Canada) dissolved in 2004. The Reform Party renamed itself to the Conservative Party of Canada. They got the wingnuts and racists to stop talking to the press.
But they kept the old Reform Party leadership. The religious right is still in control. And now they run the country.
This could be the future of the American Tea Party. Even if they destroy and replace the Republican Party, they will still be the major party of the right. And it will still be in power once in a while.