there are lots of functioning alcoholics and drug addicts out there. just cuz you can't handle your buzz doesn't mean no one can.
Yes and no. Eventually it tends to catch up with them, and they either quit the drug or flame out. The problem is that addiction progresses, and so while maybe for some number of years the addict can keep up appearances and make it seem like everything's OK, eventually the addiction gets to a point where they can no longer do that. They either have to quit, or it starts annihilating everything else in their life.
The speed at which that happens is very different for different addictions. Crack generally fucks people's lives up very quickly, but alcohol is infamously slow. It takes years to become an alcoholic, and someone who is seriously alcoholic can keep up some semblance of a normal life for perhaps 10 or 20 years before it really starts to take a toll. But, eventually it does. Things like heroin and cocaine are somewhere in between, people manage to keep up appearances sometimes for a number of years before flaming out, but like all addictions they progress too.
Crack though, and things like crystal meth, are in that category of drugs that tend to destroy people's lives and finances in a matter of years rather than decades, which is why a crack addiction is a much bigger deal for a politician than a drinking problem is. Harsh as it may be to say it, the slowness of alcoholism likely means a politicians political career will be over before it really messes them up, so it's more of a personal problem. A crack addiction is more likely to destroy their ability to function while they are still in office.