More than 100 liberal activists, leaders and celebrities signed a letter urging Joe Biden to select Sen. Elizabeth Warren as his running mate, intensifying pressure on the presumptive Democratic nominee from the left as he faces competing demands to pick a black woman.

The letter portrays Warren (D-Mass.) as the best prepared prospect to serve as president and one uniquely capable of helping Biden politically in the November election. It asserts that he is “already strong” among nonwhite voters but could use help winning over disaffected voters who acked Sen. Bernie Sanders (I-Vt.) in the primary — even as some of them have soured on Warren.

“A crisis election as big as 1932 requires a big running mate. So why not the best?” says the letter, which bears the names of an array of left-leaning figures ranging from actress Jane Fonda to leading activists such as Ady Barkan and Charles Chamberlain.

It adds, “Elizabeth Warren has proven herself most prepared to be President if the occasion arises and deeply expert on the overlapping emergencies now plaguing America — Covid-19, Economic Insecurity, Racial Injustice and Climate Change.”