Are Illinois and Delaware the only states where...

[Tintrlvr]

I think a Democrat could win Washington with just King County nowadays. In 2016, only King, San Juan and Jefferson were more Democratic than the state as a whole, and San Juan and Jefferson are very small.

Edit: Missed Whatcom, but it was only very narrowly more Democratic than the state as a whole. San Juan, Jefferson and Whatcom are all also relatively similar, so the right Republican could win all three while losing King by enough to lose statewide.

[Tintrlvr]

Rhode Island (Providence County) is another possibility. 2016 suggests even Connecticut in the exactly right splits could go Democratic with the Democrat winning only Hartford County but would be tough I think for a Democrat to win with neither Fairfield County nor New Haven County.

[Tintrlvr]

I think a Democrat could win Washington with just King County nowadays. In 2016, only King, San Juan and Jefferson were more Democratic than the state as a whole, and San Juan and Jefferson are very small.

Edit: Missed Whatcom, but it was only very narrowly more Democratic than the state as a whole. San Juan, Jefferson and Whatcom are all also relatively similar, so the right Republican could win all three while losing King by enough to lose statewide.

If Democrats are losing Snohomish they will lose state wide as well

https://uselectionatlas.org/RESULTS/state.php?year=2004&fips=53&off=5&elect=0&f=0

In addition to the above (2004 was a different era, King was much less Democratic and the Olympic peninsula much more Democratic), Snohomish was stronger for Trump and weaker for Clinton than Washington state as a whole, so obviously it is possible for a Democrat to win statewide without Snohomish.

[Tintrlvr]

I think a Democrat could win Washington with just King County nowadays. In 2016, only King, San Juan and Jefferson were more Democratic than the state as a whole, and San Juan and Jefferson are very small.

Edit: Missed Whatcom, but it was only very narrowly more Democratic than the state as a whole. San Juan, Jefferson and Whatcom are all also relatively similar, so the right Republican could win all three while losing King by enough to lose statewide.

If Democrats are losing Snohomish they will lose state wide as well

Snohomish was stronger for Trump and weaker for Clinton than Washington state as a whole.

Not true; it was weaker for both Clinton and Trump than the state as a whole, and it was more weaker for Trump than it was for Clinton.

You're right, I was misreading the results (read Trump at 35.83% instead of 36.83% statewide) Still, by less than 1%.

[Tintrlvr]

Maybe Connecticut? In 2016, Hartford and Fairfield Counties were more Democratic than the state as a whole, but Fairfield usually isn't; in 2012 it was Hartford and New Haven Counties (and New London County, very narrowly) that were more Democratic than the state as a whole. In the exact right split between 2012 and 2016, you could see a scenario where neither Fairfield nor New Haven was more Democratic than the state as a whole (but both very close to the statewide result), meaning a Democrat could theoretically win a razor-thin statewide victory with just Hartford County.

Edit: In fact, 2008 Presidential was very close to this scenario as only Hartford, New Haven and Middlesex Counties were more Democratic than the state as a whole, and New Haven and Middlesex Counties were only more Democratic by a few tenths of a percent each. Same in the 2018 Comptroller's race with Fairfield substituted for Middlesex.

[Tintrlvr]

It is mathematically possible in Arizona for a Democrat to win only carrying Maricopa County (since it has more than half of the state's population). But, currently it's the 'swing county' of the state being close to 50/50 Democrat/Republican. 

This definitely isn't going to happen anytime soon, but if rural areas continued to get more Republican and urban/suburban areas continued to get more Democratic, I could see this happening maybe 30 years from now.

Very unlikely because Pima is more Democratic than Maricopa and also quite urban. Also very hard to see the heavily Hispanic and Native American counties (especially Apache and Santa Cruz - maybe Coconino could flip, it's got a big Native population but is also driven in its D lean by a concentration of white liberals in Flagstaff and Sedona) flipping in a Democratic victory even 30 years from now.