In what part of America did John Kerry seriously underpeform expectations?

[Arbitrage1980]

The two states where he didn't do as expected: Florida (he was leading by 1-2 points in several polls going into Election Day) and North Carolina (where John Edwards didn't help whatsoever).  He was competitive in Nevada but fell short.    Interestingly, there's some discussion in the 2004 section that discusses West Virginia--in which Kerry was initially within range (how times have changed!) but pulled out resources early.

In hindsight, however, Kerry did rather well--had a significant GOTV effort (the Republicans did as well and had several anti-gay initiatives in states that got out their base).    He wasn't the greatest candidate but he did well in the debates--and he came within 118,000 votes to take Ohio and the election (and he did overperform in much of the Midwest).

wow, the 2004 election does stick out in how republican florida was (relatively speaking) compared to how it voted in 2000, 2008, 2012, and 2016.

How did bush win it by so much?

W Bush 04 was very strong with Latinos and white suburban women (the opposite of Trump 2016). In FL, he lost Miami-Dade by 7, won Osceola (Orlando suburbs) by 6, and barely lost Orange (Orlando) by 0.2. In contrast, Trump 2016 lost those counties by 30, 25, and 25, respectively. W Bush also won bellweather Hillsborough (Tampa) by 7 while Trump lost it by 7. Trump, however, outperformed Bush in the exurbs and rural areas outside of Tampa, I-5 corridor, and the Panhandle.

[Arbitrage1980]

The two states where he didn't do as expected: Florida (he was leading by 1-2 points in several polls going into Election Day) and North Carolina (where John Edwards didn't help whatsoever).  He was competitive in Nevada but fell short.    Interestingly, there's some discussion in the 2004 section that discusses West Virginia--in which Kerry was initially within range (how times have changed!) but pulled out resources early.

In hindsight, however, Kerry did rather well--had a significant GOTV effort (the Republicans did as well and had several anti-gay initiatives in states that got out their base).    He wasn't the greatest candidate but he did well in the debates--and he came within 118,000 votes to take Ohio and the election (and he did overperform in much of the Midwest).

I voted Bush 04, but people are way too hard on Kerry. He ran a solid campaign against an incumbent POTUS just a few years after the worst terrorist attack on U.S. soil. He crushed Bush at the first debate. But ultimately, Americans were not willing to change ship during a time of war.

W Bush underperformed with working class whites in the Midwest. The economy was recovering, but the Midwest remained weak while the Southwest, Texas, Florida, did better. Bush barely won Iowa, won Ohio by 2, and lost PA, MI, WI, MN.

[Arbitrage1980]

Kerry improved on Gore's numbers in several large, traditionally Republican suburban counties that ultimately went Democratic in 2008 (Loudoun, Chester, DuPage, Wake, Jefferson/Arapahoe, CO). Keep in mind that in a time of war, one might expect the incumbent President to improve on his performance in these strongholds. So in that sense, I wouldn't say he underperformed in those places.

I would say that Kerry most underperformed expectations in some of the Clinton/Bush states that weren't seen as totally gone in 2004 like AR, TN, WV, MO. The latter two states in particular because Kerry did contest them on a small scale.

In both of these ways then, the 2004 election was effectively a continuation of the trends, beginning in the late 1980s, that have brought us to the stage where we are now. As we know, in 1988, Dukakis came within 3% of winning states like Vermont, Maryland, Illinois, Pennsylvania, and California, and flipped Washington, Oregon, Massachusetts, Rhode Island, and Hawaii permanently into the Democratic column. However, Bush did better than his national averages throughout the old Confederate states.

Through 1992 and 1996, as we know, Clinton flipped all of the Bush 3% or less states-and all except Pennsylvania came permanently into the Democratic column. He also made Delaware, Connecticut, and New Jersey Safe Democratic, Maine as well (up until 2012), and turned New Hampshire and Florida into tossup states. At the same time, however, Clinton slipped in the rural South and was unable to carry a majority of Southern states. Then of course, 2000 saw a major rural breakthrough for Bush, while Gore made yet more progress in urban and suburban areas. Both these trends continued in 2004.

You forgot to mention that Kerry did flip Fairfax County, Virginia, into the Democratic column, and Fairfax County has been a vital component of the Democratic ascendancy in that state.

Yup. Kerry flipped Fairfax and Mecklenburg (Charlotte). Then Obama 08 really made serious gains in GOP suburbs, winning Loudoun, Prince William, Wake, Chester, Hamilton, San Diego. The group where Trump suffered the most relative to prior GOP candidates is college educated white suburban voters making $200K+.