washington u.s. president donald trump defense secretary plan week become first pentagon chief travel mexico independence day activities defense department say tuesday sign defense tie withstand political tensions two countries u.s.-mexican relations strain trump threats curtail trade latin america economy well demand mexico pay border wall keep immigrants drug traffickers jim mattis plan trip friday would fifth u.s. defense secretary mexico say pentagon spokesman army lieutenant colonel jamie davis secretary mattis visit mexico reaffirm commitment bilateral defense relationship north america community davis say although mexico official independence day sept. 16 celebrations take place sept. 15. event commemorate launch mexico war independence spain 1810. fact mattis would visit important national event notable mexicans long memory mexican-american war 1846-1848 lead mexico loss almost half territory unite state war long make u.s.-mexican military cooperation somewhat sensitive subject mexico visit mattis also come amid sign improve u.s.-mexican cooperation crack heroin trade reuters report april mexico army allow unite state unite nations observe opium poppy eradication nl2n1he07m mexican army take u.s. military officials helicopter tour half dozen sit sinaloa chihuahua two three state along durango make golden triangle mexican opium produce one source say time first u.s. defense chief attend mexican independence day events