Bernie Sanders is taking his campaign back to his grass-roots base Saturday with nearly 5,000 house parties for supporters as the Democratic presidential primary battle heats up.

The Vermont senator declared his candidacy two months ago – and raised more than $18 million in the first quarter, far more than any of his rivals – but has devoted his efforts to rallies and other large-scale events in the early-voting states of Iowa and New Hampshire.

Now that Vice President Joe Biden has taken the plunge with his Thursday announcement, Sanders is activating his passionate supporters.

“At the end of the day, I believe now — and I’ve always believed — that grass-roots activism is more important and more effective than 30-second television ads,” Sanders told the New York Times.

He will connect to the house parties, which are being held in all 50 states and at least 19 foreign countries, via live stream.

Biden’s first-day fundraising haul of $6.2 million edged Sanders’ total of $5.9 million in his first 24 hours as a candidate.

But Biden tapped fewer donors to get there, with 97,000 deep-pocketed contributors to Sanders’ 225,000 small-dollar supporters.