The Blue Dog Democrats are becoming more and more scarce in Congress. Two members of the coalition were defeated in primaries in Pennsylvania on Tuesday. One pundit says there's a chance the demise of the group could help Democrats down the line.

Greg Sargent argues getting rid of the moderate Democrats could have the same effect on Democrats that the Tea Party had on Republicans. How?

Sargent says Congressional Republicans are terrified to oppose their party for fear of a conservative backlash. Democrats could use the same dynamic for liberal or progressive issues.

When Republican voters ousted Bob Bennett in Utah in 2010, conservative party actors convinced every Republican politician that it could happen to them if they were labeled Republicans In Name Only, even if they were loyal to the party line on most votes. In part, this was the culmination of a multi-cycle campaign by the Club for Growth and other organized conservatives to target moderate Republicans with tough primary challengers. After the campaign in Utah and in other states with contested primaries won by right wing challengers, conservatives have always insisted that the winner won because of national conservative issues rather than any local factors or a general throw-the-bums-out feeling during a recession. The result? No Republican Member of Congress believes he or she is safe from primaries, and therefore does everything possible to avoid the RINO accusation.

If liberals want to duplicate this from the left, and make these two wins matter beyond the district lines, their work is cut out for them. They need to win the spin, and they need to keep it going in other districts this year and in future election cycles. The stakes are certainly high enough.

Imagine a scenario in which Democrats again win unified control of government — and instead of having to deal with dozens of Members who are terrified of voting for the mainstream liberal agenda, there are dozens of Members who are terrified of opposing it. Compared with 1993 or even 2009, that would be whole ‘nother ballgame.