President Barack Obama won’t see a return on the impact of his headlining speech at the Democratic National Convention until voting results trickle in come November. But the president thinks his message to Americans — to reject Republican presidential nominee Donald Trump and “do for Hillary Clinton what you did for me” — was effective, according to his speechwriter, Cody Keenan.“When it was done, what did he say?” NBC’s Peter Alexander asked Keenan.“He said, ‘I think that worked,’ Keenan recalled during an interview broadcast on “NBC Nightly News with Lester Holt.” “That’s it.”