That's the theory, anyways.Yet American is a centrist nation. The Democrats are a centrist party. Why would another centrist party not work?
Other than the fact that the idea that a nation is "centrist" is a truism, because the way a first-past the post system works - two candidates of the same type harm each other such that either the two parties much merge or one must fail, as voters gravitate to the two stronger parties out of three. A third party can only enter the arena if it can exploit the mistakes of a pre-existing major party, ultimately at that party's expense.