The betting market Intrade, a popular site for political prognosticators, is now closed to Americans. 

"We are sorry to announce that due to legal and regulatory pressures, Intrade can no longer allow US residents to participate in our real-money prediction markets," the company said in a statement Monday. "Unfortunately this means that all US residents must begin the process of closing down their Intrade accounts. We strongly urge you to begin this process immediately." 

U.S. regulators on Monday sued Intrade, saying the company illegally let customers bet on options that must be traded on regulated exchanges.

U.S. banks already barred customers from betting on Intrade. Yet the markets on American politics are the most popular, and most new accounts originate in the United States. 

Those political markets, which tend to closely follow polling, have been fairly reliable predictors of electoral outcomes. But on issues where the general populace has little useful information, the market is equally useless, as explained in this Tomorrow magazine article