“God forbid we should ever be 20 years without such a rebellion,” Thomas Jefferson wrote to William S. Smith in 1787 — the same letter that observed the natural manure of the tree of liberty is “the blood of patriots & tyrants.” Thirteen years later, the Virginian found that rebellion need not require blood: his defeat of John Adams in the presidential election of 1800 — the “Revolution of 1800,” Jefferson called it — peacefully removed a sitting government from power. The election showed that in liberal democracies, dramatic change in governance can come from ballots, not bloodshed.

This republic has experienced revolution not once, but three times in the past 20 years. In 1994, voters decided they had enough of Democratic business-as-usual on Capitol Hill and handed Congress to Republicans. In 2006–2008, voters punished Republicans for their military-adventurous and spendthrift neoconservatism by handing both the White House and Congress to Democrats. And just last month, voters decided that the change Democrats promised in 2008 was not the change the country needed. In each case, voters revolted with just cause.

The next revolt—a civil war, actually—may not be for control of government, but for control of a political movement: the Tea Party. What happens inside the Tea Party over the next several months will shape the nation’s political course for the next 20 years.

Let’s dispel a couple of myths about the Tea Party and the 2010 election. First, the movement did not inspire as many voters who oppose it as those who support it. Exit polls show that voters who claimed to support the Tea Party significantly outnumbered opponents last November.[1] More importantly, 2010 independent voters had a more favorable view of the movement than either major political party.[2]

The polls dispel a second myth: the Tea Party is not an “Astroturf” operation ginned up by corporate interests; it is a legitimate, large grassroots movement. And like other grassroots movements, it is not a unified, homogeneous organization under a central leadership and with a single political philosophy; it is a loose affiliation of people with significantly different political philosophies.

However, that heterogeneity could provide the battle lines for a Tea Party civil war. Polling data[3] indicate that Tea Party members divide roughly equally into two distinct groups: libertarians and small-government conservatives who worry about fiscal imbalances and government overreach at home and abroad, and neoconservatives and social conservatives who want government to actively pursue certain cultural and national goals.

What allowed those two groups to unite and succeed in November is their shared opposition to President Obama and Capitol Hill Democrats’ “new progressive” agenda. The small-government crowd objected to new progressivism’s cost and government intervention into matters they consider private, while neoconservatives and social conservatives want government to undertake a very different set of interventions.

What happens now, when the Tea Party can no longer simply oppose the country’s political leadership, but instead must provide some of that leadership? It will be difficult to maintain its internal alliance if neoconservatives and social conservatives start pushing their own activist agenda while small-government conservatives and libertarians demand less government.

Civil war can be averted if the Tea Party’s two factions find common cause on a policy agenda. Returning the federal government to fiscal sustainability is a goal of both factions. A government focused on its core duties would please small-government conservatives while satisfying neoconservatives’ concern for national security. A renewed commitment to civil liberties would delight libertarians while protecting social conservatives’ freedom to (privately) follow their conscience. A policy agenda focused on those goals would maintain the Tea Party alliance and be highly attractive in an increasingly diverse nation.

There is also opportunity for alliances between the left and some Tea Partiers. New progressives and neoconservatives could join together, resulting in a movement akin to original progressivism with its heavy-handed government interventionism both at home and abroad. Or the left could abandon progressivism and rediscover liberalism (that is, advocacy of civil liberties and concern over the concentration of power — foremost in government), finding common cause with libertarians and small government conservatives.

The Tea Party’s success means that it must now change — either through internal conflict and division or by uniting around a commonly embraced agenda. The course it chooses will determine the long-term viability of the movement and its effect on American politics.