Following incidents in San Bernardino last year, it is not only your iDevice which is at risk. The Visa Waiver Program for entry into USA was also changed so that even if you have applied under the Electronic System for Travel Authorization, you must have an biometric Passport (one with a chip in it). If your passport is old and was issued before they had chips, you will need to apply for a new passport.
You may choose your own flavour of British press to look further, but the Grauniad goes on to say
As part of its restrictions the US also implemented changes to prevent foreign nationals who have travelled to Iran, Iraq, Libya, Sudan or Syria from entering the country without a visa. It also denied automatic visa waivers for foreigners who have dual Iranian, Iraqi, Sudanese and Syrian citizenship.
I would imagine that that second item is based on self reporting. I don't know the status of those who go to these countries in military campaigns -- I am guessing that that happens without a passport or immigration status -- but I certainly hope that that US is not restricting entry to those who fought in Iraq as part of the Coalition of the Willing™.
