Jeff Weaver: When Biden runs a campaign around electability, 'you have to win elections'

04:17

Jeff Weaver, senior adviser to Bernie Sanders's campaign, join Andrea Mitchell to discuss Trump attacking Sanders, lower than expected turnout in Iowa, and his thoughts on rivals Joe Biden and Mike Bloomberg, the latter of whom he calls 'the billionaire backstop' attempt to stop Bernie Sanders from winning the nomination, though he thinks that 'Democratic voters are going to reject that.'