I think it not just his physical, but also mental feebleness.
His handlers are scared stiff he’ll go off script….again.

Biden’s Team Lashes Out at Trump for Planning a 4-State Tour Next Week – Jealous Biden is Too Feeble to Travel and Campaign.

President Trump will visit four states next week as the Democrats hold their DNC convention.

Trump is planning on visiting Pennsylvania, Wisconsin, Minnesota and Arizona.

In an extra jab to Biden, President Trump plans on visiting Biden’s hometown of Scranton, Pennsylvania next Thursday — the same day Biden is scheduled to ‘virtually’ deliver his acceptance speech.

Team Biden isn’t too happy about Trump’s plans to travel and go out and meet voters.