This is late, but I've been wanting to say something about it for awhile.
Letter From Senate Republicans to the Leaders of Iran
The whole ridiculous letter to Iran from Senate Republicans is here:
It's condescending, ostentatious, threatening, egotistical and pretty much a pack of lies. But Obama folded anyway. The Republicans intended to conduct diplomacy on behalf of a foreign power (ISRAEL, in case you missed it) with Iran outside of diplomatic and official and presidential channels, but they ended up crippling the president more directly (and helping their bedfellow, Israel). Why do liberals have to be so darned reasonable?? I don't expect a stunt like this from Democrats when the Republicans gain control of the White House. And not only because they'll go to war at the drop of a hat and before trying any kind of diplomacy!
Here is the best rundown on all the lies and implications of the Republican letter to Iran:
Also, 10 Frightening Facts About Tom Cotton, the architect of the stunt.