There's also the issue that, in the Sum of all Fears scenario with a Mark-12 nuclear bomb (12-14KT) you can knock out the White House, Capitol Hill, or the Pentagon, but it's really hard to even get two of the three with a ground burst. I've attached a nuke map run for a bomb that tries to go for both the Pentagon and White House. The Capitol is safely outside of the blast or radiation. In terms of the White House, it's no longer the about-to-fall-over structure from before the Truman renovation, so 5 PSI may not do it, and the Pentagon as a structure is almost certainly surviving. You can get 1/3 buildings completely, and maybe get 2/3, but it's likely the inhabitants inside these buildings survive if they don't get killed from glass. So, this won't be a full decapitation of DC, and most of the line of succession will be in place. What's more, even though losing the Pentagon is a huge blow, up at full war time, you already have your decisionmakers dispersed. You're losing some five stars, but your field organization is still deployed and ready to go. So, whether you choose the President without the Pentagon, or the Pentagon with the Speaker of the House as the new President, this doesn't really knock out the line of succession.
View attachment 487782