As Krugman suggests, recent years have seen the bar set pretty low for what can get a person branded as a traitor. In a February 2003 editorial, the now-defunct New York Sun called for police to monitor protesters opposing the invasion of Iraq "with an eye toward preserving at least the possibility of an eventual treason prosecution," for giving "aid and comfort to the enemy," a crime that in the United States carries the death penalty.
A few months later saw the release of a bestselling book by conservative commentator Ann Coulter (who, incidentally, holds a law degree), that insisted that American liberals – that is, about one fifth of the US population – are guilty of treason. Those who peacefully opposed the war were similarly maligned throughout the burgeoning right-wing wilds of the blogosphere, and were, it should be noted, extensively spied on by the US government.
So now a few environmentalists have envisioned the state wielding its coercive power against those who doubt that humans activity is destabilizing the Earth's climate.
James Hansen, who heads NASA's Goddard Institute for Space Studies and is regarded as one of the world's leading climate scientists, last year called for CEOs of oil companies to be put on trial for crimes against humanity for their well-documented efforts to spread doubt about global warming.