By MATTHEW LEE, AP Diplomatic Writer DAKAR, Senegal (AP) — Traveling across Africa, U.S. Secretary of State Antony Blinken saw firsthand the limits of America’s influence abroad. Blinken confronted authoritarianism, growing threats from newly energized extremists, and persistent challenges posed by COVID-19 and climate change, all of which have stubbornly resisted various U.S. interventions. And, nowhere