Washington (CNN) A nonprofit executive who campaigned on offering "Medicare for all," stunned the Democratic establishment and secured one of the activist left's biggest wins yet Tuesday in a House primary in Nebraska.

Kara Eastman defeated the better-known former Rep. Brad Ashford, a "Blue Dog" who argued for compromise, by nearly 3 percentage points.

Ashford was seen by the Democratic Congressional Campaign Committee as a strong fit for a district that is slightly to the left of the nation's average -- voting for President Donald Trump by 2 points in 2016 and Mitt Romney by 7 points in 2012.

Now, the national party is left grappling with whether Eastman's win will hurt their chances of ousting Republican Rep. Don Bacon, who had been seen as vulnerable in November.

Tuesday's stunner in Omaha was a major primary victory for the left and underscored the momentum behind progressive and female candidates within the party, even as groups that have backed similar candidates, such as EMILY's List for women and Sen. Bernie Sanders' "Our Revolution" group for progressives, sat out the race.

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