A mixture of unusually strong Jewish support as a result of the Lieberman nomination and this being part of the country where you really can (not sure about nowadays -- although possibly -- but certainly in the 1990s/2000s) get a substantial crossover vote from normally-Leans-R voters by emphasizing gun control really hard.
Lieberman probably helped in this part of the world, especially among Jews, although Gore paid dearly for that pick elsewhere.
Did he? Lieberman was probably part of what made Gore so relatively strong in FL too, after all. It's easy to suggest with hindsight that Gore might've won if he'd picked Shaheen or Graham, but it's tough to know what calculations the Gore team was making at that time.
These are the states where the 2000 election recorded the highest Democratic lean of any election of the 1992/1996/2000/2004/2008 stretch:
It doesn't look
obvious to me that Lieberman was a terrible pick, necessarily.
