He had 12 years in elected office, first as a state senator, then as a US Senator. Before that he spent pretty much all of his time since graduation thinking* about how to acquire power and what to do with it after getting it. And just what is a "community activist"? He was a ward heeler - a cog in a political machine. His time as a community activist gave him the experience he needed to win an Illinois senate seat against native black Chicagoans with sharp elbows.
In retrospect, Obama's no flash in the pan. In terms of political skill, he's the Democratic Reagan, a guy who patiently learned the political trade and ultimately defeated the Clinton brain trust during the 2008 primaries. And his strategy for re-election was to set up an expensive operation in battleground states that employed party cadres (aka community activists) to perform constituent service, thereby giving the locals a reason to turn out for him. This is retail politics at its most basic and used to be standard issue practice in most big cities, financed as it was via political corruption. These days, I assume it's financed by PAC and union money, to avoid career-ending FEC problems.
* This stuff is detailed in his books and the biographies - friendly and otherwise - about him. There a lot of rhetoric about how he's a moron, incompetent, and so on. I think that's wrong. He's not incompetent or a moron - he's an ideologue. The guy's raw IQ is probably similar to GWB's, and that would stand to reason, given his dad was a Harvard guy and his mom had a PhD, back when colleges had standards, and women PhD holders were as scarce as hen's teeth.
I beg to differ. Barack was a groomed, celebrated figurehead. He did nothing on his own accord.