A Democratic strategist said he wishes Hillary Clinton had started courting the millennial vote — a demographic won by rival Bernie Sanders during the primary campaign — earlier in the campaign and said turning the younger part of the Democratic base out for Clinton will be “key” to her success in November.

“There was some effort during the convention to reach out to this group, but I think everyone went to sleep for two months on our side,” former Massachusetts Democratic Party Chairman Phil Johnston said today on Herald Radio. “She had to raise money, so she was absent from the trail over most of August.”

Johnston said the $50 million banked by Clinton in August will help with television ads in the swing states, but said winning over younger voters with only 39 days until the election will be a challenge.

“I think that’s a key demographic left for Hillary Clinton to nail down and it’s not an easy one because they are alienated from both candidates and from the system to a larger extent,” he said. “They have witnessed the economic meltdown, they are having a hard time paying for college, they are worried about healthcare, and worried about getting jobs that are going to be able to support them.

“Bernie, I think, will be key to Hillary’s success,” Johnston added. “But it is late in the game to be doing this work. I wish they had started earlier.”

Sanders appeared with Clinton on the campaign trail yesterday in New Hampshire, a state with four electoral votes where the Democratic nominee has a single-digit lead over Donald Trump.

Johnston also said the enormous amount of money spent on the campaign — Clinton alone is expected to top $2 billion spent on her White House bid by Election Day — is another factor alienating young voters who want campaign finance reform.

Nonetheless, the former state party chair said, Clinton has the platform to win over most of the youth vote.

“She has a message that is basically Bernie’s message that resonated during the primary campaign,” Johnston said. “My hope is the vast majority of millennials will come back to the Democratic pool and not either stay home on Election Day or vote for (Libertarian nominee Gary) Johnson or (Green Party nominee Jill) Stein.”