How old is too old? The question could decide several Democratic primaries

In many ways, Janet Mills is the ideal Democratic recruit to take on Republican Sen. Susan Collins, a fifth-term moderate with a track record of beating well-funded challengers. Mills is a two-term governor with a history of outperforming her party and a record of pushing back against President Donald Trump.

​ In many ways, Janet Mills is the ideal Democratic recruit to take on Republican Sen. Susan Collins, a fifth-term moderate with a track record of beating well-funded challengers. Mills is a two-term governor with a history of outperforming her party and a record of pushing back against President Donald Trump. Read More Breaking News, Latest News and Videos | CNN