WASHINGTON — The longest, loudest standing ovation of the Kennedy Center Honors gala wasn’t reserved for Al Pacino, Mavis Staples or the Eagles. Instead, it went to the man sitting to their left, attending his eighth and most likely his last honors presentation: President Barack Obama. While politics were absent from the tributes to the performers who were recognized for influencing American culture on Sunday night, the arts community’s affection for Obama — and its nervousness about President-elect Donald Trump — was palpable in the Kennedy Center Opera House. The president and first lady Michelle Obama were introduced last, after Pacino and his fellow honorees: gospel singer Staples; pianist Martha Argerich; singer-songwriter James Taylor; and Don Henley, Timothy B.