Brian Kolb announced he was stepping down as minority leader of the state Assembly on Friday, three days after he drove his state-issued vehicle into a ditch near his upstate New York home.
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An Ontario County sheriff's deputy administered field sobriety tests, which Kolb failed, officials said.
Kolb issued an apology the next day.
"This was a terrible lapse in judgment, one I have urged others not to make, and I take full responsibility for it," he said in a statement.
The arrest came one week after Kolb wrote a column in the upstate Daily Messenger newspaper warning against people driving under the influence during the holidays, and noting that December is National Drunk and Drugged Driving Prevention Month.
On Friday, he issued a new statement, according to media reports, "I have always tried to put the needs and best interests of our Conference ahead of my own. That is why I have decided to step down as Minority Leader."
"The events of December 31 are ones I will always deeply regret. On a personal level, I have begun the process of seeking professional help in order to heal, learn, and fully address the challenges that I, along with my family, currently face," he said.
Kolb has represented his district since 2000 and has served as Assembly Republican leader since 2009.
Dareh Gregorian is a politics reporter for NBC News.