Pakistan's fragile democracy, and the semblance of stability it brings to this troubled nuclear-armed Muslim country, is once again under threat. Protesters loyal to cricketer-turned-politician Imran Khan and Canada-based Sunni cleric Tahir-ul-Qadri have paralysed Islamabad for almost two weeks, demanding the resignation of Prime Minister Nawaz Sharif. The protesters' cult-like devotion to their leaders risks translating into violence, which could result in intervention by Pakistan's powerful military.

Mr. Khan is known for his anti-Americanism and support of the Taliban. He claims that a tainted vote brought Mr. Sharif to power last year and demands fresh elections. Mr. Qadri, on the other hand, espouses Sufi Islam and is outspoken in condemning al Qaeda and other terrorist groups. He says that Pakistan's isn't a real democracy, so it must be overthrown through a people's revolution with him at the lead.

Such instability is the last thing the country needs. Mr. Sharif was elected barely 15 months ago, marking the first transition from one civilian leader to another in Pakistan's 67-year history. His government promised to rejuvenate the economy with IMF-backed economic reforms, normalize relations with India and stop trying to impose Islamabad's will on neighboring Afghanistan.

Yet Mr. Sharif dithered before launching military operations in June against Pakistani Taliban in the tribal areas bordering Afghanistan, and he has been indecisive in dealing with jihadist extremists, some of whom have ideological ties to members of his Pakistan Muslim League party.The prime minister has also insisted on trying former military dictator Pervez Musharraf for treason over his suspension of the country's constitution in 2007. That move smacks of personal vendetta, since Mr. Sharif's last stint as prime minister ended in a 1999 military coup carried out by then-Gen. Musharraf.

The Musharraf trial has brought the prime minister in conflict with the Pakistani military, which has ruled the country on and off for 33 years and wields tremendous influence even when civilians lead the government. But the generals know that launching a military coup would risk the loss of much-needed international support.

Still, most Pakistanis believe the generals have given a wink and a nod to Messrs. Khan and Qadri in hopes that their televised demonstrations and threats of violence will sap the civilian government's energies. The military—and its ubiquitous Inter-Services Intelligence arm—used a similar strategy against the previous civilian government, led by President Asif Ali Zardari of the Pakistan Peoples Party.

Mr. Sharif is vulnerable partly because he governs more like a monarch than a democrat, putting family members and retainers in key government positions. Finance Minister Ishaq Dar is the father-in-law of Mr. Sharif's daughter, while the prime minister's brother Shehbaz is chief minister of Punjab, Pakistan's most populous province. Mr. Sharif also tends to encourage polarization by refusing to compromise with political opponents, a shortcoming that his predecessor Mr. Zardari avoided along the way to completing his full five-year term.

These flaws notwithstanding, Mr. Sharif's premature removal from office would undermine Pakistan's fledgling democracy. If a few thousand demonstrators are able to force out an elected leader or provoke another coup, no elected civilian government would be able to survive similar intrigue in the future.

Pakistan's fragility should concern Americans and others who recognize the country as an epicentre of global terrorism. Islamabad's preoccupation with corruption allegations and hyper-nationalist rhetoric distracts vital attention from the larger threats of rising extremism, increasing religious intolerance and widespread violence.

In the past, the United States has alternated between sanctioning Pakistan and showering it with economic and military aid to encourage civilian government and counter-terror cooperation. But the main beneficiary of such aid has been Pakistan's military, which remains unwilling to drop its strategic focus on permanent conflict with India and as a result has continued using jihadist militants as proxies for regional influence.

The Obama administration has by and large ignored the political turmoil in Pakistan as part of its general retreat from foreign affairs. In doing so, the U.S. runs the risk of facing future crises without viable policy options, much as it has with Egypt since 2011. Washington should put its weight behind Pakistani democracy, discourage Pakistan's generals from manipulating protesters and nudge Prime Minister Sharif toward a more inclusive governing approach.