Joe Biden has mostly faded into the background since he passed the baton to Kamala Harris in an unprecedented bait and switch.

While the White House has yet to explain his shocking decision to forgo re-election, Biden's brother has confirmed what many suspect.

In stunning comments to the media, Frank Biden said that declining health forced his brother's hand. The comments sparked a furious response from Biden's family.

Biden's brother on health

Joe Biden stepped down a little more than three weeks after a disastrous debate in which he showed unmistakable evidence of mental decline. His team initially shared the shocking news of his decision in a letter online.

Three days later, in a speech from the Oval Office, Biden conspicuously omitted his reason for stepping aside. His press secretary maintained his health was not a factor.

"It has nothing to do with his health," press secretary Karine Jean-Pierre said. "I can say, no, that's not the reason."

In comments to ABC, Frank Biden said his brother's decision "boils down to" his "overall health and vitality" but also "beating this genuine threat to our nation in the form of Donald Trump."

Somewhat ominously, he told CBS of his brother, "Selfishly, I will have him back to enjoy whatever time we have left."

A source close to the Biden family lashed out over the comments, saying, "Frank Biden suffers from alcoholism and hasn't spoken to his brother in weeks."

Coverup under scrutiny

While Harris' campaign has grabbed the media spotlight, questions remain about Biden's health and the effort to keep his decline hidden from the American people.

Republicans have been reminding voters that Harris observed Biden up close throughout his time in office, alleging she was part of a coverup. Some have suggested that Harris is, or has been, functioning as the de facto president.

While she has no known health issues, Harris has so far failed to appear for an unscripted interview, leading to comparisons with Biden's 2020 "basement campaign."

At a press conference Wednesday, President Trump challenged Harris to three debates and criticized the way his former rival was pressured aside.

"The presidency was taken away from Joe Biden, and I’m no Biden fan," Trump said. "From a constitutional standpoint, from any standpoint you look at, they took the presidency away."