1984 United States presidential election in Idaho

The 1984 United States presidential election in Idaho took place on November 6, 1984. All 50 states and the District of Columbia, were part of the 1984 United States presidential election. State voters chose four electors to the Electoral College, which selected the president and vice president of the United States. Idaho was won by incumbent United States President Ronald Reagan of California, who was running against former Vice President Walter Mondale of Minnesota. Reagan ran for a second time with incumbent Vice President and former C.I.A. Director George H. W. Bush of Texas, and Mondale ran with Representative Geraldine Ferraro of New York, the first major female candidate for the vice presidency.

The presidential election of 1984 was a very partisan election for Idaho, with just under 99 percent of the electorate voting for either the Democratic or Republican parties, and only four parties appearing on the ballot. Every county in the state gave Reagan an outright majority. Reagan's weakest county, and Mondale's best, was Shoshone County, which Reagan won 50.2%-48.3%. It was the only county Reagan did not win by double digits. Reagan's best county was Madison County, which Reagan won 92.9%-6.6%. This was Mondale's worst showing in any county nationwide.

Idaho weighed in for this election as 27.75 percentage points more Republican than the national average and with 72.36 percent of the popular vote, made it Reagan's second strongest state after neighboring Utah.

Reagan won the election in Idaho in a landslide, with a winning margin of 46%. His 72.36% vote share made it his second-best state in the nation, after neighboring Utah. The Mountain West in general had begun trending Republican in 1952, after having been a swing region that was critical for Democrats' hopes of winning the presidency between 1896 and 1948. In Idaho, this happened relatively quickly; in 1964, Barry Goldwater came within less than 2% of carrying Idaho, his closest near-win in the country. However, the trend accelerated, in Idaho and elsewhere, in 1980, as the incumbent president, Jimmy Carter, had been widely perceived as carrying out a 'war on the West' with his water, energy, and development policies. That year, Reagan exceeded the vote shares Eisenhower had received in 1952 and 1956, and that Nixon had received in 1972, in Idaho, despite garnering only a bare majority nationally. In 1984, he improved even further, becoming the first (and thus far, the only) nominee of either party to crack 70% in the state since William Jennings Bryan in 1896.

Reagan exhibited strength throughout Idaho. He got over 60% in all six of its most populous counties--Ada (Boise), Canyon (Nampa), Bonneville (Idaho Falls), Bannock (Pocatello), Kootenai (Coeur d'Alene), and Twin Falls (Twin Falls). In four of the six (including Ada, by far the largest), he got over 70%; and in one (Bonneville), he exceeded 80%. Amongst smaller counties, Reagan did particularly well in heavily Mormon southeast and south central Idaho, winning over 90% of the vote in Madison County (his strongest performance in any county in the country), and over 80% in Jefferson, Franklin, Cassia, Clark, Bear Lake, Caribou, Fremont, Minidoka, and Oneida Counties. However, his strength in the state was broad as well as deep; in only one county (Shoshone) did he fail to run up a double-digit margin over Mondale. Mondale's strength, relatively speaking, was concentrated in and around the Silver Valley region; he was able to break 40% only in Benewah, Latah, Nez Perce, Clearwater, and Shoshone Counties. This election is the most recent election in which the winner won every county in Idaho.