There is no First Amendment right to "intimidate, coerce, threaten, or harasses a foreign official . . . in the performance of his duties".
There is every right to protest someone verbally - especially a tyrant, and especially when Bush had just told Hu to let his people speak freely.
At worst, this is a disorderly conduct charge. Not this.
Telling Hu he should stop killing Falun Gong is harassment? Well, I guess it is interfering with his "official duties"...
I'd reccommend doing some reading on our reaction to the Stamp Act, or to the seizure of Hancock's ship "Liberty". Given that by that time British officials operating outside the review of colonial legislatures may be counted as foreign officials, the lessons of our Founding are most applicable here.