The victory of David Brat, a little-known Tea Party-movement candidate, over House Majority Leader Eric Cantor in Virginia’s 7th District Republican primary in June shocked many political analysts. Yet since 2009, Tea Party candidates have defeated several Republican incumbents and threatened many more. They forced the shutdown of the federal government last year and almost forced the U.S. government to default on its debt. What accounts for the movement’s success?

The Tea Party is a decentralized, populist movement that formed in 2009 in response to the financial crisis and the election of Democratic President Barack Obama. While the movement is fragmented, its members are generally united in their beliefs in limited government, free markets, low taxes, and individualism and in their intense negative views of President Obama and the Democratic Party. At the height of the Tea Party’s popularity in 2010, a CBS/New York Times poll showed that some 55 percent of Republicans supported the movement.

The movement’s success in the past five years is due in part to its highly engaged, politically active supporters. The Tea Party movement is also supported and funded by national conservative political organizations such as the Club for Growth and by wealthy individuals who advocate rolling back government programs and market regulations. In addition, the movement is aided by conservative media outlets, which have raised the movement’s profile and tried to fuel the discontent of its activists.

The Tea Party movement has benefited from the primary process, which allows voters to elect their party’s nominee and in which fewer voters tend to participate. Redistricting and demographic changes, which have made many House districts more homogeneous with respect to party affiliation, have also aided the movement. Several House seats have become so firmly Republican that the more ideologically extreme Tea Party candidates can challenge Republican incumbents and, even if they do not win, force incumbents to take positions further to the right.

The movement has also built its popular legitimacy through appeals to the Constitution. Many Tea Party activists argue that the Constitution was divinely inspired and embodies eternal and unchanging principles. Their views are based more on ideological convictions than on historical evidence. The Constitution was built on compromise, not divinely inspired unity among the Founders. Moreover, while the Founders believed in limited government, they sought to strengthen the role of the federal government and to better regulate commerce and the money supply in order to provide greater stability.

The Tea Party also uses populist and nationalist rhetoric, railing against big businesses, the federal government, and immigrants—stances that have resonated with the increasingly conservative Republican base.

The movement has shifted the Republican Party’s focus from cultural and social issues to economic issues such as reducing the federal debt and cutting government programs. Its biggest impact, however, has been to make it more difficult for the Republican Party to govern. The Tea Party does not have a positive policy agenda. It is an opposition movement. Supporters view compromise as a sell-out and see those who do compromise as enemies.

Tea Party legislators have intentionally sought conflict with President Obama, the Democratic Party, and their own party leadership. This has made it nearly impossible for the Republicans to work with Democrats to pass legislation. Even within the Republican Party, House Speaker John Boehner has found it increasingly difficult to find a majority and has put issues like immigration reform on hold.

In the Senate, individual Tea Party senators have blocked legislation and nominees with the threat of a filibuster. In this way, the Tea Party movement has contributed to further gridlock in Congress. While creating conflict and gridlock may be a conscious strategy by the movement, it has led to growing cynicism, frustration, and apathy among much of the American public.

The Tea Party’s uncompromising positions and confrontational style have cost it some support. A CBS/NYT poll in June 2014 showed that only 21 percent of Americans and 36 percent of Republicans supported the movement. The movement has also alienated some mainstream Republicans, who view the Tea Party’s views on immigration, the Federal Reserve, the debt ceiling, and the Export-Import Bank as too extreme.

The Founders established the American political system as a framework to find collective agreement among multiple interests. The system is built on compromise and incremental policy change. The Tea Party’s goals are conflict and radical change. Its main legacy will be to make it increasingly difficult to find collective solutions and increase political and economic instability.