Donald Trump argued that radio host Glenn Beck — who has endorsed Ted Cruz — can't vote for Cruz in his state's primary Saturday because he is no longer a registered Republican.

For Trump, this provides proof that Beck is "dumb as rock." Beck appears likely to still be able to vote for Cruz in his state of Texas, however.

"Word is that crying @GlennBeck left the GOP and doesn't have the right to vote in the Republican primary. Dumb as a rock," Trump tweeted Saturday.

If true, this would serve as rich irony for some observers. Trump has been hit for his fleeting party affiliation history, but is, by all accounts, currently a registered Republican in his home state of New York. The deeply conservative Beck, however, actually left the Republican Party in March 2015, citing frustration that the establishment was blocking the efforts of lawmakers like Cruz.

It is unclear whether Beck ever formally registered as an independent, or other party, thus deregistering as a Republican.

But it might not matter.

Beck principally resides in the suburbs of Fort Worth, Texas, and is presumably registered to vote there. Texas is considered an "open primary," however, meaning non-Republicans like Beck can vote there.

"I've made my decision — I'm out. I'm out of the Republican Party," Beck said in March 2015. "I am not a Republican."