If I could go back in time, and if I could take modern technology with me.
I would go back and "help" our founding fathers to be less vague on some topics.
I would set up defensive Vulcan machine guns to protect Pearl Harbor from the attack of Dec. 1941, I would hand over the specs for the early jet fighters and early air to ground and air2air missiles, to combat the Germans and the Japanese, I would try to advise using the A bomb except as a last resort, avoid the Cold War by giving Patton the tanks of today for his use against the Russians.
I would exterminate the Anti Semitic behavior of the modern Arab nationalism by exterminate those who preach it.
I would watch and intervene against those who use the Communist threat to further their own brand of political terror.
I would use the power, hopefully benevolently to heal ,to cure, to build.
I would use that time too to see my grandmother play pro baseball, to see my paternal grandfather, to see my uncle before he left for duty in Japan( he was killed in Korea).
The thing is we do have real time travel, but only forward.
Its our kids,our grandkids, we teach them right and wrong, how to think, how to love and to forgive, hopefully we then can see a bright future.