I've been struggling to understand the harm in the creation of these new institutions, or why the US would pressure allies not to join. The best I can come up with is an analysis I read a day or two ago, that the fear is that China will lend money to various emerging markets through these institutions (leveraged up by its dupe cash-cow partners), and when the projects inevitable fail to produce sufficient cash flow to cover the debt, China will offer to forgive the debt in return for certain "favors" (political, military, economic).
It seems extremely far-fetched to me, and would take over a decade for such a plan to come to fruition, but who knows what the Obama administration is thinking these days. Personally, if China wants to lend more money for infrastructure, I'm all for it. And if anyone wants to join them, I can't see why that would harm us. If anything, the faster GDP growth that better infrastructure would enable would only help us economically, but creating more consumption and demand for our products. The bonus is that the US could finally free-ride off of Chinese efforts, instead of the reverse scenario of the last 30 years.
Clearly, I'm missing something.