Sick President, Dude
National security implications of Trump with COVID:
Pence sequesters himself immediately. Thanks to the asymptomatic nature of COVID he may already have it.
If Trump's condition deteriorates, command authority (the little suitcase with the nuclear codes) goes to Pence. This is done routinely in the case of mild impairment such as dental work. This will almost certainly happen very quickly if it has not already to protect the military attaches responsible for maintaining this, because while you sign up for a lot of risk in the military, voluntarily exposing yourself to a fatal disease is usually not on the list.
If Pence is also infected with COVID, the constitution mandates the next on the list to be Nancy Pelosi. Thanks to politics being what it is, this will almost certainly be bypassed if possible and go to the ranking cabinet member (Mike Pompeo). This would also most likely trigger a constitutional crisis were it to be made public, despite Pelosi likely having zero desire to be responsible for running a possible war against North Korea.
If you're scared at these options (you should be), thanks to the nature of this administration there ARE no good options. This is why we have elections!
If you live outside the United States and are enraged that this pack of failsons and grifters could be serially responsible for the destruction of the planet, yes, that's correct. As can Putin's cabal of mobsters, whoever Xi Jinping hasn't managed to kill as a likely successor, whomever still hasn't managed to kill Boris Johnson, three bureaucrats Emmanuel Macron may be passingly familiar with, Benjamin Netanyahu's more insane coalition partners, a joke I'm not qualified to make about Imran Khan, a joke I'm not qualified to make about Narendra Modi, and Kim Jong-Un's sister. As a bonus joke, China's official policy is to launch a nuclear strike on warning, and nothing wrong with that has ever happened.
Speaking of elections, if either Trump or Biden (or both) pass away before the election, their names would still be on the ballot. It would be up to the electoral college at that point to determine who actually is named President. If they cannot decide, the House of Representatives. If they can't decide, welp.
Basically, this.
https://www.youtube.com/watch?v=hSyQvrb-caQ