I don't blame Lehane. It was a great political move and Bush could have put this fire out back in the spring and it would have been forgotten.
Everyone knew he had a drinking problem and the revelation that it caused him legal problems wouldn't be shocking. In fact, many looked up to how Bush was able to turn his life around with the help of his faith in God and Jesus Christ. That his problem reached breaking the law would make his comeback (and climb up) even more impressive.
The ideal time to have disclosed this was the 1994 race for governor. He was running against Ann Richard, who also had overcome a drinking problem. The Lieutenant Governor was Bob Bullock who was also a reformed drinker. There is no way the issue could have been used against him that year.