“This field campaign will make sure primary voters know that Ed MarkeyEd MarkeyWHIP LIST: How many Dems will back Sessions? Confirm Inga Bernstein for the District of Massachusetts FCC takes aim at AT&T, Verizon over 'zero-rating' services MORE is the only candidate in this race that has written some of the most historic environmental legislation ever considered by Congress. When voters know about Ed Markey’s record of being a champion in the fight to address the climate crisis and stand up to Big Oil, they’ll send him to the United States Senate to fight for them,” said Navin Nayak, LCV senior vice president of campaigns, in a statement.

LCV is spending at least $650,000 on the effort, and plans to knock on the doors of at least 219,000 likely primary voters in Massachusetts. The group's political action committee, LCV Action Fund, endorsed Markey early on in his campaign and has since raised or contributed more than $100,000 to Markey's campaign.

The canvassing effort for Markey's primary alone amounts to about half of what LCV engaged in to help elect Warren; the group spent more than $870,000 and knocked on 400,000 for her campaign.

Markey faces a challenge from Rep. Stephen Lynch (D-Mass.) for the Democratic nomination to replace Secretary of State John KerryJohn KerryKerry: Trump can’t instantly undo Obama actions ‘All or nothing’ leaves us nothing Kerry: Trump comments on German chancellor ‘inappropriate’ MORE (D), and he entered the race — and remains — the front-runner. A recent poll put Markey ahead of Lynch by nearly 30 percentage points, and he has the backing of a number of big-name Democrats in Washington and Massachusetts, including Kerry himself.

Whoever wins the April 30 Democratic primary will likely go on to win the general election in June; though there are three GOP contenders vying for the party's nomination, the eventual nominee is unlikely to win in a state as blue in Massachusetts.