A few other factors have also contributed to increases, according to the report:
"The more aggressive tactics of the past two years, two senior intelligence officials told NBC News, were sparked by a string of domestic incidents in 2015 and 2016 in which the watch list system and the FBI failed to stop American citizens from conducting attacks. The searches also reflect new abilities to extract contact lists, travel patterns and other data from phones very quickly."
In case you were wondering, Borders and Customs agents can search you and confiscate your stuff at airports and border crossings without the having to meet the requirement of at least reasonable suspicion that's normally needed for such searches within the US. They even have the right to take your devices for five days without any justification, although officials must return them to you if they lack probable cause, according to the report. In other words, there's a chance your experience crossing the border -- even as an American citizen -- can be a complete nightmare and potentially a days-long pain in the ass, so if you're traveling internationally any time soon, you may want to brace yourself.