Bush seemed out of touch w/ the electorate, for example when asked by reporter what was the cost of a gallon of milk, his answer was embarrassingly wrong -- and worse, low...
The economy was in a recession, people were seriously worried about it going from bad to worse. Bush supported NAFTA, which was unpopular w/ working class folks who feared exportation of American manufacturing jobs to Mexico.
Bush was widely quoted following a speech in which he affirmed America's role in building the "New World Order." He was TALKING about the US's new role as world's only superpower following the collapse of the Soviet Union, but to his skeptics this became a euphemism for a sinister cabal of wealthy industrialists finally consolidating their conquest of the Earth.
He was never the best public speaker -- he was to Reagan what Al Gore was to Clinton. By the time the presidential debates came around, he was demoralized by his drop in approval and it showed in his uninspiring delivery. Clinton, by contrast, was an excellent, polished speaker, consistently on-message and confident.
He even admitted to having problems expressing "the vision thing." He was portrayed as kind of a dork by a number of sources in the press. He threw-up on a Japanese diplomat. He sometimes butchered the language in his speeches. He had to defend against a "wimp factor."
He was criticized for choosing Dan Quayle as his running mate in 1988, and retaining him in 1992. Quayle was perhaps the most notoriously poor speaker in the history of US politics. He frequently made unintentionally hilarious gaffs. Making fun of Dan Quayle was a major cottage industry during Bush's term in office.
In his 1988 campaign, Bush promised he would not be involved in raising taxes. He said "Read my lips. No new taxes." Then as the economy floundered he raised taxes. This alienated some of his core supporters.
But Bush probably would have won if not for H Ross Perot's remarkable third party campaign. Perot appealed to (sorry to have to use the word) Conservative voters -- people who opposed NAFTA, opposed new taxes, wanted the focus to be on domestic issues. So he siphoned more votes f/ Bush than f/ Clinton.
The following were (at the time) lesser criticisms of Bush. These were not so much related to why he lost the election as they were just extra rumblings hovering in the background.
The Savings & Loan debacle happened on his watch. This was a $150 BILLION (in retrospect, because it was financed over time some say it will ultimately cost the tax-payers $400 BILLION) bail-out for S&L's that had taken advantage of Reagan-era deregulation to finance land deals that went south. The fed felt it had to bail-out investors at the expense of the taxpayer to ensure that the banking system would not collapse.
Bush had been involved peripherally in the Iran-Contra scandal. This was a deal the CIA had brokered with Iran whereby the US would sell weapons to Iran in exchange for oil, then the oil would be more or less laundered through Israel, converted into cash and the cash used as a slush fund to fund CIA operations in Nicaragua. At the time, Nicaragua was ruled by the Sandinistas, a party that the US had supported in their rise to power in the late 70s. But in a Castro-like move, the regime went Socialist, nationalizing industries (which means that the industries American stockholder's had their assets in Nicaragua seized by the gov't.) The Contras were the new revolutionary organization.
Also at some point in his career, Bush had been the head of the CIA, which is a position of authority that many Americans do not trust. The CIA is often regarded as cavalier about flouting laws and dodging oversight in pursuit of national interests. This is probably partially true -- secrecy goes hand in hand with intelligence operations. However it is spurious to suggest that his involvement with the CIA automatically made Bush corrupt.
In the background of all this is the incident at Ruby Ridge. It didn't make mainstream news until the following year when the stand-off in Waco, TX resulted in the destruction of their compound and the deaths of most of the Branch Davidians, but in 1992 the ATF (Alcohol-Firearms-Tobacco) had a stand-off at Ruby Ridge resulting in the deaths of a rifle-wielding 14-year-old and an unarmed pregnant woman. The law-and-order policies of the ATF were a legacy of the Reagan years (and bi-partisan "tough on crime" legislation,) when funds were pumped into the military and law enforcement agencies, and they were given increased authority to prosecute those who found in violation of gun laws. In effect, the increased authority of the ATF was a corollary to the never-ending War on Drugs.
Eventually the political fall-out of the increased powers of these law enforcement agencies fell into the laps of Clinton and Janet Reno. Since then the ATF has played it cool, but a significant chunk of Americans are now less trusting of zealous law enforcement agencies.
Also the Waco stand-off was Tim McVeigh's rationale for orchestrating the OKC bombing in 1995.
Just as his presidency was winding down Bush authorized increased military presence in Somalia, a nation that had recently fallen into anarchy. Clinton inherited this problem too, and the result was depicted in 2001's "Black Hawk Down." In late 1992 the nation was in more economic duress than in 1990 and was less sympathetic to the plight of the Somalis than that of the Kuwaitis, so the military action did nothing to increase Bush's popular support.
