Maine Governor Janet Mills announced Thursday that she is suspending her U.S. Senate campaign, citing insufficient financial resources to continue her bid for the Democratic nomination.

Mills' withdrawal comes just weeks before the June 9 Democratic primary, where she was set to face Graham Platner, an oyster farmer and former Marine running his first political campaign. The governor had received backing from the Democratic establishment in Washington.

Mills stated she no longer had the "financial resources" necessary to compete effectively in the primary race. Her departure from the contest virtually assures Platner will secure the Democratic nomination without a contested primary.

Both Mills and Platner were seeking to challenge five-term Republican incumbent Susan Collins in what has become one of the most closely watched Senate races in the current election cycle. Collins has held the seat since 1997 and is considered a key target for Democrats.

Platner, who combines military service with his background in Maine's seafood industry, now appears positioned to become the Democratic standard-bearer in November's general election against Collins. The race is expected to be highly competitive and could play a significant role in determining control of the U.S. Senate.