It's worth noting that in the United Kingdom, you can already be fined or jailed for tweeting. Neither of these would be criminally actionable offenses in the US, and the first one especially would be clearly protected political speech:
There is a huge degree of difference between being denied entry to a foreign country and having punitive action taken against you by the government.
Your second case is about a guy who was thought to be making immediate threats, rather than simply tweeting something offensive, and he was released after the grand jury refused to indict him on free speech grounds:
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
I don't see the word citizen in there at all. While the courts generally agree that it only applies to citizens, it is definitely not obvious.
http://www.bbc.co.uk/news/uk-england-leeds-19883828
http://www.theguardian.com/uk/2012/mar/27/student-jailed-fab...