NAIROBI — Residents in this capital city were on lockdown as President Obama arrived Friday evening for a three-day visit, leaving many already chafing under tight security measures meant to reduce crime and minimize terrorist threats.While his arrival was heavily anticipated because of his Kenyan roots, the streets were unusually quiet in this normally bustling, chaotic metropolis. No groups of young men were hanging on corners, pedestrians were absent, beggars moved elsewhere.
