Tunisia's President Beji Caid Essebsi takes the oath of office at the constituent assembly in Tunis December 31, 2014. (Zoubeir Souissi/Reuters)

Vance Serchuk is an adjunct senior fellow at the Center for a New American Security.

Tunisia is rightly hailed as the lone success story of the Arab Spring: the only country that has threaded a path from the uprisings of 2011 to genuine multiparty democracy today. Yet the future of freedom in Tunisia is far from assured. With the election of a new parliament and president in recent weeks, the most important experiment in Arab democracy is entering a difficult and potentially perilous new phase — one in which greater U.S. support and attention are urgently needed.

Tunisians are quick to cite a litany of challenges that could still derail their transition, including an unreformed economy that generates too few jobs and a persistent threat from terrorist groups such as Ansar al-Sharia. There’s also the failed state next door in Libya, a volcano of Syria-like potential that threatens to kick up a cloud of instability over its neighbors.

Yet easily the most significant question facing Tunisia concerns its new elected leadership and its commitment to democratic principles, human rights and inclusive, tolerant governance.

These have been the hallmarks of Tunisian exceptionalism since 2011, thanks in large part to the parties and personalities that have been at the helm of the transition. Special credit goes to Ennahda, the moderate Islamist party that captured the largest number of votes in the country’s first free election three years ago.

At the time, there were doubts whether Islamists could really operate according to democratic rules. But in marked contrast to the Muslim Brotherhood in Egypt, Ennahda passed that test with flying colors.

Rather than aggrandizing power, Ennahda shared it — forming a coalition with two leading non-Islamist parties. Rather than running roughshod over secular opponents in writing a new constitution, it compromised and made concessions while respecting civil society, free media and an independent judiciary.

Most important, Ennahda did something no ruling Islamist party has done: It peacefully left office.

At the root of Ennahda’s conduct was the conviction of its leader, Rachid Ghannouchi, that democracy means no single party — regardless of how popular — has the right to dominate society and that it is necessary to find common ground with your political adversaries. The alternative is either civil war or authoritarianism — which is sadly where much of the rest of the region has ended up.

But Ennahda now finds itself out of power, with a new anti-Islamist party, Nidaa Tounes, having won the presidency and relegated Ennahda to second place in parliament. Will Tunisia’s secularists practice the restraint, tolerance and inclusivity that its Islamists demonstrated?

It remains to be seen. The concern is less about Tunisia’s new president, Béji Caïd Essebsi — who ably led the country in the chaotic months after its revolution and delivered a hopeful message of national unity at his inauguration this week — than about others around Nidaa Tounes whose democratic instincts may be less developed.

In addition, many Tunisians across the political spectrum — including staunch opponents of Ennahda — tell me they are worried that Persian Gulf countries that have been supporting anti-Islamist campaigns in the region may try to extend those efforts to Tunisia — offering aid in exchange for a democratic rollback, potentially including politicized prosecutions of Ennahda members.

Optimists counter that Tunisians, having recently overthrown a dictator, won’t tolerate authoritarian backsliding. Yet the history of revolutions underscores this risk; just consider the trajectory of post-Soviet Russia or Georgia more recently.

Ultimately Tunisia’s destiny will be determined by Tunisians themselves. But democratic powers have a vital interest in reinforcing at least one toehold of decent, pluralistic governance in the Arab Middle East and North Africa. If there is a legacy of hope and change in the Arab world the Obama administration can help secure, it will be here — and the coming months will be key.

First, top administration officials and members of Congress need to prioritize Tunisia, despite competing crises. They can start by simply showing up — visiting Tunis to make clear to the new government U.S. openness for significantly expanded partnership in light of Tunisians’ unique achievements, provided the country stays on the democratic path.

Equally important is to engage Ennahda and civil society, to reassure them that the United States recognizes their historic contribution to Tunisia’s progress and will be watching closely how they are treated, as a litmus test for the new government. And we must press our European allies to deliver the same message.

Finally, the United States needs to put forward a multi-year package of economic, security, trade and governance support for Tunisia — including low-cost but potentially high-yield investments in the workings of new democratic institutions such as the parliament.

Although the United States has found creative ways to help Tunisia since 2011, the effort has been too small-scale and ad hoc. In the Obama administration’s budget request this past year, Tunisia ranked ninth among bilateral aid recipients in the Middle East and North Africa — exactly the same position as the year before its revolution. There is something fundamentally wrong if this persists.

Over the past three years, Ennahda’s Islamists proved themselves to be responsible stewards of a free society. Now it is the turn of Tunisia’s ascendant secularists to do the same — and the responsibility of the United States, and our democratic allies, to help all of Tunisia succeed.