The answer depends on if you are limiting the time period to recent history. And your definition of terrorist. The only recent known attempts to smuggle a bomb into the US across our border is from Canada. If you include drug smugglers though it’s highly likely bombs have come across the border or some bomb parts. However if you consider the Mexican Revolution and Pancho Villa, ect. a lot of bombs came across the border and also went from the US into Mexico.
The answer depends on if you are limiting the time period to recent history. And your definition of terrorist. The only recent known attempts to smuggle a bomb into the US across our border is from Canada. If you include drug smugglers though it’s highly likely bombs have come across the border or some bomb parts. However if you consider the Mexican Revolution and Pancho Villa, ect. a lot of bombs came across the border and also went from the US into Mexico.