More than 76,000 migrants crossed the U.S.-Mexico border without authorization in February, breaking records for the fourth time in five months. Border enforcement authorities warned Tuesday that the border is hitting a breaking point: Government facilities are full and agents are overwhelmed. The numbers from February are more than double than levels from the same period last year. “The system is well beyond capacity, and remains at the breaking point,” Kevin K. McAleenan, commissioner of Customs and Border Protection, told reporters. More than 90 percent of the new arrivals are from Guatemala, officials said. Large groups of arrivals are now much more common, as they are diverted by new restrictions at many of the leading ports of entry. At least 70 groups of 100 or more people have turned themselves in at Border Patrol stations that typically are staffed by only a handful of agents. Only 13 such sizable groups arrived last year.