"artık" is anymore/as of now/from now on/no longer. There are a lot of was to translate depending on context, but I guess the key here is that something has changed. There is another sentence "Duo artık işsiz" which means, "(As of) now, Duo is unemployed". Poor guy must have just been fired. (Wait, you can't fire a president... he must have quit, lol)
"şimdi" is now, as in this very moment, but doesn't imply change. "Şimdi randevum var." I have appointments all the time, and one of them happens to be right now.
I know you waited a long time for a response, but I hope it helps you or someone else with the same question :-)