The one state that he lost was Minnesota, which was Walter Mondale's home state, and he only lost it by the slimmest of margins, like 5,000 votes or less I think.

In 1984, the US was riding on a wave of good feelings after a rocky start to the Reagan administration. The Economy was finally making a recovery after nearly a decade of "stagflation" much of which was blamed on Jimmy Carter, there was a surge of patriotism as Reagan tried to rally Americans against the Soviet Union, and for the first time people actually felt positive about their future and the future of the country. These sorts of feelings were summarized in the theme of Reagan's re-election campaign "Morning in America".

On the other side you had an opponent in Walter Mondale who the Reagan campaign was able to successfully paint as a weak willed liberal who wanted to raise taxes, back down to the USSR, and take us back to the Carter years (People back then REALLY hated Jimmy Carter). Mondale also made the fatal mistake of flat out promising to increase taxes.

The race was sort of close as Mondale attempted to portray Reagan as feeble and old and unable to continue to run the country. Reagan nullified this attack through a few zingers during the debates, and from that point it was pretty much over for Mondale, Reagan was re-elected in the biggest electoral landslide in US history.