Not That Difficult
Here's Biden's problem, and I think it's clear enough that even he recognizes it. The slimmest of Democrat majorities in Congress have shielded him from investigations over the past two years. If he loses either house in the November elections, Republicans will control key oversight committees with subpoena power, which will at best threaten his prospects in 2024 -- but there are potential avenues of investigation that could reach a "Nixon standard". This phrase has come up in connection with potential Trump offenses that could have been uncovered in the Mar-a-Lago raid (but so far have not) -- but I'm not the only one who's seen parallels between Nixon and Biden as well. A quick web search suggests that there's never been a clear definition of a "Nixon standard" for impeachment, but of course, Nixon was never impeached, so his case can't be a precedent anyhow. Nevertheless, legal scholars in the Clinton impeachment came up with this ...