The argument is shifting anyway.
Step 1: The impeachment of a former president is unconstitutional.
Response: But hey look, here are a bunch of constitutional lawyers, including conservative ones, who say it's constitutional.
Step 2: Okay, maybe it's constitutional, but it's a waste of time.
Response: There has to be some kind of consequence for presidents who do illegal and harmful things during their lame duck periods.
Step 3: Well, in any case, Trump never specifically told his legion to storm the Capitol, destroy property, cause deaths, etc.
Response: Based on everything he's been saying for the past year about election fraud, and how he doubled down after he clearly lost the election, and how he called people to show up to protest on the day of, and stoked their unfounded passion to "save the democracy" and "stop the steal," a very reasonable argument could be made that he incited the insurrection.
Step 4: Well, even if he incited it, he was just exercising his free speech!
Now that you've pointed out that "incitement of violence" is not a protected form of speech, I wonder what the next step in the shifting argument will be?