W/o speculation or hindsight, how do you prove, in terms of deaths and economy, how much better shape we'd be in were a liberal in charge?

it is inherent that no actual proof is possible since the situation can not be replicated to test other policies.

what can be done is look at the actual experience of other nations and speculate that, if we had prepared the way they did [starting ten or more years ago], had a population willing to follow government orders, and had the systems and laws in place to aggressively follow up on all positive reports of CV19, then we might have held deaths down to very low numbers as Iceland and Singapore are doing.

Of course, this requires either a dictatorial government willing to use police to enforce health restrictions, or a great deal of trust in the government [Iceland has this, America does not].

It is a pointless exercise, imho. We have the government we have because that's all the people would allow. America is not going to accept apparently arbitrary orders from government officials ... civil insurrection would be the likely ultimate result.

Are you new here?

Only speculation I'm ding right now is how many lives were lost, due to states banning drugs. Only becouse Trump mentioned them by name.

Historically, liberals have had success with the Great Depression, the bush depression, World War II, social security, Medicare, and Obamacare, among others. Historically, Liberals are much better at running big government programs and dealing with large national problems. Conservative successes are generally on a small scale.

leftists are in charge, they prevented our border fence even after they approved it...

Just look at what Obama and Clinton did. They both inherited recessions, with unemployment above 7%, from PEEpublican presidents. They turned things around. By the time they left office, unemployment was less than 5% in both cases. The swine flu, or H1N1 virus, did not cause a recession under Obama because he took it seriously. Trump is still downplaying the threat and dragging his feet dealing with the Covfefe-19 virus pandemic, firing people, such as the captain of the aircraft carrier, for alerting Americans to the seriousness of the situation. He wants to know the name of the official who sounds an alarm about how critically the government is short on medical supplies, so he can presumably fire him/her, instead of using the Defense Production Act to order manufacturers to make more surgical masks and gowns. Nurses are using plastic garbage bags to protect themselves, and Trump says that there is no shortage of medical supplies. That is simply outrageous and dangerous.

Look at liberal run NYC

There is no way to prove that. All you can do is speculate. 

If a liberal was in charge, the economy wouldn't have been good as it was before the pandemic, which means the economy crashing would have been more harmful to America. However, that is my speculation.

Uh, wouldn't that be speculation?

You can't.   Until the Chinese Virus, Trump led the best economy in generations.