With nearly all of Iraq’s political forces lined up against Iran in 2018, it looks likely that the pro-Iranians will be trounced at the ballot. And yet it looks just as likely that this will have little effect on Iran’s influence in Iraq.

In Iraq’s electoral system, it’s very difficult for any one alliance to take much more than 20 percent of the vote. This means the various alliances must engage in horse trading and coalition building to form a government. As parties try to secure lucrative ministries, they will lose sight of the goals that they campaigned on — like Iraqi independence. Like every government formed since the invasion in 2003, the next one will be made up of parties pulling the country in different directions. It is a recipe for inaction — and Iran will prey on this.

Neither the United States nor Saudi Arabia nor any other country will be able to have a decisive influence. Outside countries have consistently failed to positively influence Iraqi politics. If these parties really want to prevent Iranian influence, they should provide assistance to security units, like the Counter Terrorism Service, which has been by far the most effective force against the Islamic State. The continued success of professional security services, rather than Iran-backed paramilitary groups, will allow for Iraq to guarantee its own security.

Against this backdrop, there remains one wild card that could present a real challenge to Iranian domination: intervention by Grand Ayatollah Ali al-Sistani, Iraq’s Shiite spiritual leader.

In 2014, Ayatollah Sistani issued a fatwa that called for Iraqis to defend the country against the Islamic State. In response, tens of thousands of Shiites joined the army and other groups, including pro-Iranian paramilitary forces. The fatwa’s unintended effect was to give these groups some form of religious legitimacy. Many commentators have speculated that Ayatollah Sistani may now be on the cusp of rescinding his fatwa, which could, in turn, force the Popular Mobilization Forces to dissolve.

For now, that seems unlikely. The Popular Mobilization Forces enjoy broad legitimacy for their contribution to the war effort, and many Iraqis prefer that they be maintained as part of the official security forces. Even Mr. Abadi has opposed any such dissolution for many of these same reasons.