The use of military-style power in Ferguson, Mo., has galvanized a coalition of libertarians and liberals calling for curbs on the use of force by police—a partnership that departs from the party-line splits that have long dominated American politics.

The alliance that has arisen in the wake of protests over the police shooting of an unarmed black teenager in Ferguson is the latest in a growing list of issues where liberals and libertarians have found common cause. The scope of National Security Agency surveillance, U.S. drone policy, criminal sentencing and corporate power all have emerged in recent months as topics of concern among both liberal Democrats and libertarian quarters of the GOP.

These instances of agreement hardly signal an end to partisan gridlock in Washington. Liberals and libertarians remain fundamentally at odds over basic policy questions such as government safety-net programs and federal regulation. But their occasional alliances do point to new political dynamics as national policy debates shift from the tax-and-spending issues that so easily split along party lines—and as the growth of libertarian sentiment within the Republican Party has created new coalition-building opportunities.

"It's too bad it takes a crisis like this [trouble in Ferguson] or the NSA revelations a year ago to get people to notice the problem of overreaching government," said David Boaz, executive vice president of the Cato Institute, a libertarian-leaning think tank.

Laura Murphy, director of the Washington legislative office of the American Civil Liberties Union, said that her traditionally liberal group has been cultivating closer ties with libertarian-leaning conservatives like Sen. Rand Paul (R., Ky.) because they are an increasingly significant voting bloc that can help advance the ACLU's legislative agenda in Congress.