Former White House doctor and now Rep. Ronny Jackson (R-TX) said Sunday on Fox News that President Joe Biden's cognitive decline is progressing quickly and putting the US "at great risk."

"[The decline is] happening quickly," Jackson told "Sunday Morning Futures" guest anchor Sean Duffy.

"Like you said, I've taken care of three presidents… so I know firsthand what it takes to be the commander-in-chief and the head of state. It's a grueling job, both mentally and physically. This man can't do the job. He's proven to us every single day that he can't do the job, but this is going to get worse."

Jackson has been talking about Biden's decline since the 2020 presidential campaign, but the COVID-19 pandemic shoved many campaign events behind a camera, and Biden was able to hide much of the decline at that point.

"Unbelievable"

Now, Biden is 81 and the oldest president ever to serve, and further decline has set off alarm bells among the electorate.

"It's just unbelievable how much he's degenerated just during his time in office. We cannot afford to have this man in office for the remainder of this term and then [for] another four years after that. He's already putting us at great risk right now," he said.

It seems that many voters agree. Polls have been saying that Biden is "too old" to serve another term for the majority of 2023, and Biden now trails former President Donald Trump in swing states like Pennsylvania, Georgia and Arizona, according to polls from such liberal sources as the New York Times.

National polls are also favoring Trump over Biden, with the latest NBC poll putting Trump four points ahead of Biden.

No clear replacement

Jackson has been saying for a while what most Democrats don't really want to admit.

Earlier in the month, Jackson said again on Fox News, "I've been saying for quite some time now, when he was candidate Joe Biden, that I didn't think that he had the cognitive ability to do the job."

Some Democrats have said Biden should not run in 2024, but no clear replacement has emerged.

Former First Lady Michelle Obama has been put forward as a viable replacement, but she has said previously that she won't run.

California Governor Gavin Newsom (D) is obviously very interested in jumping into the race if Biden bows out, but he barely beat a recall in 2021 and is also white and male.

It would likely be problematic to choose Newsom over Vice President Kamala Harris, but the party could justify Michelle Obama, who is also a woman of color.