Trump already disproved that notion. Trump did tremendous harm, mostly because he insisted on trying to govern through EOs instead of, ya know, passing bills. Yes, they did get the SCOTUS, but that was mostly McConnell. Trump made us a laughing stock, he weakened our alliances, he strengthened/emboldened our enemies...the list is pretty long.

Better than Clinton, if you're a Republican.

It doesn't matter how ineffective your party's candidate is. If they do nothing in their four years in office, it's still better for what you want than letting the opposing party have four years in the chair. All of the appointments, all of the department heads, all of the policy decisions - even if they're not advancing your goals, at least they're not reversing things you want.

Again, if your views of what's good for the country lean strongly towards the GOP perspective, then even the worst of Republicans is better for the country than even the best of Democrats. For a bury-the-needle conservative like McConnell, he'd rather have Trump in office than Biden any day of the week and twice on Sunday - even though he'd rather have any Republican other than Trump.