As mentioned only Congress has the power to allocate funds. The trick here is to fund the $400 and I can't see any source of money that can be tapped by EO to do this so it must only be a political ploy for the re-election and looking at the polls it is working. Like many of his ideas they are unconstitutional such as barring US citizens from entering the country if they are sick which violates the 5th Amendment on free movement. A President can write EO's that can do anything whether legal or not but if it costs money their hands are tied. The legality of particular EO's can and will be challenged in court or Congress can pass an ACT making the EO illegal assuming a 2/3 majority. The Court question usually runs afoul of the complainant's legal standing to bring suite. I am unsure if regular citizens have standing so it probably must come from Congress and can be expedited to the SCOTUS. The question is whether Congress is willing to do that in lieu of an alternative palliative for the people which apparently is impossible to get through both Houses.
What all of this does is manifestly make it clear that the US can and will print money for anything which is a scary policy by either party. There are only a few tools available in an economic crisis of this magnitude. The first is to lower interest rates to zero...done! The second is to prop up the banks and equity markets with free and easy money...done! The next is to print sufficient money to float the people...insufficiently done
The last is austerity and this hasn't even been discussed. The elephant in the room is the military budget which is so bloated it is shocking. Cutting the military back to post-Vietnam levels and budgets is not only necessary it is existential to the survival of this country past this emergency which will end eventually. But, apparently cutting the military is taboo and we are embarking vigorously towards 2 new war fronts in Lebanon and Belarus. Someone has to pay for all of this.
The next huge trick is to keep inflation low and I just don't see any tools left in the bag to do this. If you flood markets with newly minted dollars it must result in inflation.To get back to normal everything must re-open but in ways that keep people safe enough. Getting people back to work is imperative and it is going to require creating new jobs. If the military gets whacked it will put back into the job pool roughly half a million more. Not a huge number considering the population of 330 million.
If you look at Sweden as an example of doing absolutely nothing about COVID-19, it has returned already to very low numbers. Yes they had a high death rate but they are more or less over and done with the virus and things have returned to normal. What most people fail to understand is that eventually everyone is going to get exposed to this virus. It is only a question of when. Only a vaccine will be effective in stopping this pandemic and personally, as a vaccinologist myself I will take any vaccine that is safe enough even if it is only 35% efficacious which is enough to stop a pandemic. Having worked at USAMRIID for a long time I received 21 unlicensed vaccines to work there and many had side effects that were almost as bad as the diseases themselves. I am alive and well so it didn't hurt me long term and I am probably a good example of normal. Also, roughly 65% of infected with COVID-19 don't get sick and the remaining 35% are the at-risk population usually with comorbidity diseases, so eventually this virus is going to burn itself out and I predict it will be roughly next Spring after large segments of many countries receive a vaccine which is imminent (January for the Russian vaccine should it pass the Phase III safety trials) whether it be Russian, Chinese, British or American. IMHO the Oxford vaccine holds the most promise but I will get the Russian one as soon as it is available here in Hungary which is already signed up to get the vaccine and to possibly produce it here. On a side note I worked over 10 years in former Soviet Republics and spent some considerable time analyzing the vaccines produced in the Soviet Union and most were fine. Many were not very good with efficacies in the 30% range but for those disease (plague is an example) these are the only vaccines anywhere on the planet. The Pharmaceutical industry of capitalist countries is not geared to design, test, or produce vaccines that are not profitable. Only countries that are willing to invest state funds and resources are able to develop these kinds of vaccines. The US military has a requirement to develop these orphan vaccines for soldiers deploying to high risk areas but Congress has never funded the military enough to do this work. Hence the minimal levels of vaccines since WWII. Most, like myself, have retired and left the industry entirely. None of us were replaced.