to be precise, I believe Haig said, "I am in charge here ... at the White House." He didn't say he was in charge of the country (as the liberal press distorts his statement). He did specifically mention the White House and I believe at the time, he was the senior person there. He may have stated that way to try and calm things down. If you remember that day, the press was quite crazy with rumors and questions. It wasn't a big deal, but the press went stupid over it.
In the mid-80's I was at a luncheon where Al Haig was featured speaker. He joked about the "I'm in charge" quote at his own expense. Had a sense of humor about it and put people at ease.