Why was 2000 so close?

[un]

This is gonna be long.

Before 1992, the Democratic Party wasn't doing very well. Most people viewed their presidential candidates as "too liberal", and even if they voted for Democrats to be in Congress, they would prefer Republican presidents.

However, that changed in 1992, when the economy was doing poorly, and the Democrats nominated a moderate, Bill Clinton. People were generally sick of the GOP status quo that had been going for 12 years, and they didn't just go to Clinton, they also went to Perot, including some liberals. However, Clinton would end up winning, thanks to his ability to win over enough of the liberal base in the Democratic Party, as well as win over Reagan Democrats, a base of generally moderate and blue collar Democrats who voted Republican in 1980, 1984, and even some in 1988, due to what they viewed as the Democrats being too liberal. With Clinton, they came back, and gave him a Democratic congress to boot.

However, people didn't love the full Democratic government, particularly Clinton's healthcare bill pushed by Hillary, which the Republicans labeled socialism, and used their momentum to win the 1994 midterms by a landslide, taking the house and senate. Now Clinton had to work with Republicans, and was forced to do some stuff that liberals did not like, such as the 1996 welfare reform.

With the 1996 election approaching, many thought that Clinton was done for, after all, he just came after a crushing loss in the midterms. However, the country was doing well economically, and generally, they liked Bill Clinton around this time, and saw little need for a GOP president, or Ross Perot, though he did have a base of around 8%. However, they didn't really see a need for a Democratic congress either, so in 1996, Bill Clinton won easily, and the Republicans held their majorities.

During his second term, Clinton was popular, despite the Lewinsky scandal and the impeachment later, the economy was strong, and he was generally liked. The 1998 midterms was also a big disappointment for the Republicans, they didn't win any senate seats and lost seats in the house, leading to Gingrich resigning, who was unpopular at that point. However, many also saw Bush as the inevitable successor, as many Americans wanted a "moral leader" again, and his last name certainly helped.

Gore was the Democratic candidate, the VP of Clinton, and he easily won the primary over Bill Bradley, despite a close race in New Hampshire, he swept the rest of the primary. The Republican primary was also a big win for Bush, but it did have a more moderate anti-establishment base in votes for John McCain.

Going into 2000, the Democrats had established a permanent expansion in their base. With the Republican Party moving to the right, they held an advantage with moderate voters, did better with Hispanic voters, and expanded into winning groups long won by Republicans, such as Asians. They did all of this while holding onto their liberal base, allowing them to compete nationwide with the GOP. However, Gore would also turn off some voters, mainly blue collar white voters. This was largely over issues related to guns, the environment, and moral issues. Bush and the GOP knew that, and took advantage of that, appealing to that base in states like Arkansas, Tennessee, West Virginia, Georgia, etc. They also held onto their base in the western states and very wealthy suburbs, which were generally Republican leaning at the time. They also benefited from many Cuban voters, which were already a Republican group, protest voting for Bush due to the Elian Gonzalez custody issue. This created an environment of competition between the two parties, and it ended up being decided by a couple hundred votes in Florida, which meant that the Cuban swing was in all likelihood, consequential.

TL;DR: The Democrats had a permanent expansion in their base going in 2000 thanks to the Clinton years, but also lost some of their base to the GOP based on guns, environment, and moral issues, leading to a close election environment.