Yes, if indeed there is some reason that a president would need to be impeached before he could be tried in a court of law then sure, all he needs is a small group of senators that have no interest in impeaching him and he can go full Caligula. 

My confusion is this, I have no clue why Trump's lawyers would make this argument other than it is a bid to give a president the powers of Emperor of the Universe. 

I don't see nor understand what impeachment has to do with criminal prosecution of obvious crimes. Where did they come up with that argument? 

To me, it openly appears as two distinctly different things, impeachment, a tool provided our Congress to remove a corrupt or dangerous person from office and criminal prosecution in a court of law a function of our justice system. 

Impeachment is just the removal tool, the way the Congress can remove a dangerous criminal, like Trump, from office when he does something like inciting a violent insurrection against our government.

I do not think, and neither do Republicans as Dan points out earlier in this thread, that you have to impeach the president to prosecute him in a court of law...as they were saying they did not need to impeach him because they believed he COULD be prosecuted in a court of law once he left office. 

So, I was just saying I do not understand how the argument Trump's lawyers made could in any way be valid. It sounds to me like it is idiotic and nonsensical. However, I am not a lawyer and so I am not sure if my common sense approach to this is correct.