CNN guest Tia Mitchell warned Monday afternoon how the energy behind Vice President Kamala Harris’ presidential bid could “run out” if the campaign didn’t release a firm platform addressing her policy proposals soon. Mitchell appeared on “CNN News Central” as she discussed Harris’ potential campaign platform and focused on Harris’ higher polling among voters for the economy despite President Joe Biden’s low polls. While Mitchell explained how Harris has been benefiting from not being blamed for the economy under Biden, she warned how the “enthusiasm” around the Democrats’ “hopeful and positive…