According to The Washington Post (the article in question is here), "the Biden campaign on Saturday condemned Trump’s decision to sidestep" signing "a loyalty oath requested of candidates for election in Illinois that asks, among other things, to swear that they won’t support overthrowing the government." (Requested, not required, the piece points out.)
Who knew?
According to the Post, the oath dates back to the McCarthy era of the 1950s and "remains enshrined in Illinois law" even though it's been ruled unconstitutional by federal courts.
The paper helpfully notes "other candidates, including President Biden and Florida Gov. Ron DeSantis (R), filed signed oaths along with their petitions, according to the local media reports."
Naturally, five Illinois residents have already petitioned the State to remove Trump's name from this year's Republican primary ballot.
(No word on whether any of the five are Republicans, or whether Trump's name is even on the ballot at this point…but hey, it's 2024.)