Democrats asserted the war in Iran was costing Americans dearly, citing the deaths of more than 10 military personnel and a sharp increase in fuel prices.
Top Democrat members have endorsed the protests, calling on Americans to hit the streets in protest against Mr Trump’s immigration policies.
Mr Biden’s letter comes as a defiant response to calls from top Democrat lawmakers for him to step down after a debate against former President Donald Trump.
Last Friday, Mr Biden, 81, in a tweet declared, “I’m the nominee of the Democratic party. I’m staying in the race.”
