Editor's note: Donna Brazile, a CNN contributor and a Democratic strategist, is vice chairwoman for voter registration and participation at the Democratic National Committee. She is a nationally syndicated columnist, an adjunct professor at Georgetown University and author of "Cooking With Grease: Stirring the Pots in America." She was manager for the Gore-Lieberman presidential campaign in 2000. The opinions expressed in this commentary are solely those of the author.
(CNN) -- For many political observers, last night's loss by Eric Cantor was one of the biggest shocks of our political careers.
The Republican House majority leader was easily defeated by an almost unknown challenger whom he heavily outspent. It's been reported that Cantor's team spent more on steakhouses than his opponent did on his entire campaign.
No one had a clue this was about to happen, including Cantor himself. Just days before the primary, his camp leaked an internal poll showing him ahead by 34 points. No House majority leader has lost a primary since the position was created in 1899.
While the result was unexpected, it confirms something we already knew. In the Republican civil war, the tea party has won.
It's more than just Cantor's loss.
A week earlier, Sen. Thad Cochran, R-Mississippi, was forced into a runoff by tea party candidate Chris McDaniel. And the Republican primary winner in Maine's 2nd Congressional District is closely connected to Gov. Paul LePage and his disastrous tea party agenda that has hurt the state.
And even the candidates who are supposed to be the establishment have been pulled so far to the right by tea party challengers that there is no difference in their policies or rhetoric.
Mitch McConnell held off his primary opponent only by leaving no room for him to run, opposing anything and everything offered by President Barack Obama. Now, as the embodiment of partisan obstruction in Washington, he'll have trouble against Alison Lundergan Grimes, a mainstream Democratic candidate.
As majority leader, Cantor guided House Republicans' vastly out-of-touch agenda. Perhaps that is why it was so difficult for political operatives to believe that he could be defeated by a challenger alleging that he was not conservative enough.
Cantor has gone out of his way to set an agenda that appeals to the Republican Party's tea party wing, at the expense of middle-class families who could have benefited from the preferred mainstream approach of Democrats. But apparently, he was just not extreme enough for today's GOP.
The repercussions of Cantor's loss will reverberate for Republicans.
Their far right agenda is already hurting them in general elections. I shudder to think what Republican presidential contenders will say in a 2016 primary to win over voters who think Eric Cantor isn't conservative enough.
But even this year, the effect will be felt. We're only about halfway through the primary calendar. In addition to the Mississippi Senate runoff, Iowa's 3rd Congressional District will hold a convention next week to select their candidate. The last time the state used a convention, we wound up with Rep. Steve King.
On Tuesday night, New York Republican Peter King expressed his fear that the results "will move the party further to the right, which will marginalize us further as a national party." He doesn't need to look any further than his home state to see how the tea party is relegating the Republican Party to the sidelines.
We'll also see how Cantor's loss affects tea party primary challenges this summer in New Hampshire and Arizona.
The Democratic Party and its candidates remain committed to helping provide economic security to middle-class families and addressing serious issues such as commonsense immigration reform.
Meanwhile, Republican Party one-upsmanship to appeal to the tea party base threatens to keep their party in the minority and out of the White House for the foreseeable future.