After the imprisonment this month of the opposition leader Aleksei Navalny, punishing Russia is back on the agenda. On Monday, European Union foreign ministers agreed to impose sanctions on Russian officials, with the final details to come.

Yet such measures are unlikely to satisfy the Kremlin’s critics. They have in their sights a pet project of President Vladimir Putin’s: Nord Stream 2, a pipeline under the Baltic Sea that would supply natural gas directly to Germany.

The project has already survived fierce opposition from many European countries and the United States. And Germany, for which the pipeline is part of Europe’s delicate geopolitical balancing act, is committed to finishing it. With fewer than 100 miles to go, construction is nearly complete. But the treatment of Mr. Navalny and his supporters has once again thrown open the question of the project.

The pipeline’s predecessor, Nord Stream 1 — which was completed in 2012 and also runs undersea directly from Russia to Germany — was controversial, too. Germany’s eastern neighbors feared that Russia might cut off their gas while continuing to supply Germany. In that case, Eastern Europeans would be left to face the Kremlin alone.

But since Nord Stream 1 was finished, Europe’s energy landscape has been transformed. Although Russia supplies around 40 percent of Europe’s natural gas, largely via pipelines running through Belarus and Ukraine, it is no longer the dominant force it once was. In much of Eastern Europe, where gas used to be shipped almost exclusively from Russia, many countries, including Poland and Lithuania, now buy liquefied natural gas from the United States or Norway.

What’s more, the gas infrastructures of European countries are far more interconnected, and a European Union antitrust case against Gazprom, the Russian state-owned company that supplies the pipelines’ gas, has eroded its monopoly power. This means that Nord Stream 2 will have a marginal effect on most European countries’ energy security. It would, in practice, not alter much — which makes it all the more attractive a target for those who wish to check Russian influence.

There is one obvious loser from the pipeline: Ukraine. Much of the Russian gas currently shipped to Europe travels through the country. But if Nord Stream 2 is completed and Russia substantially reduces the gas sent through Ukraine, Kyiv would lose over a billion dollars a year in transit fees. Already a victim of Russian military and economic pressure, that would be an additional blow to the country.

That should be enough to move Germany, a supporter of Ukraine, to cancel the project. But there are plenty of other reasons, too. Few of Germany’s allies support the pipeline, with French leaders the latest to call for its cancellation. Many Europeans see it as a glaring example of German hypocrisy, as Berlin demands that other Europeans play by E.U. rules as it cuts side deals with Moscow.

Perhaps worse, a new pipe carrying fossil fuels under the sea fits poorly with Germany’s self-image as a green energy leader. Chancellor Angela Merkel’s explanation that the pipeline — funded and built by a Russian state-owned company — is a “commercial project” makes Berlin’s policy look only more cynical.

So why does Germany want the pipeline? Supporters in Berlin make two arguments. First, they say it will provide gas to replace coal and nuclear power, which Germany is phasing out. Second, they argue that buying gas from Russia will moderate the Kremlin’s foreign policy. Neither argument is especially compelling.

It may simply be that Ms. Merkel — who this month again ruled out junking the project — has clung to her pipeline for so long that it is now impossible to give it up. Although the Green Party, which will almost certainly play a role in the country’s next coalition government, is dead set against Nord Stream 2, most German politicians seem to agree with her.

That puts Berlin at odds with the United States, which has already slapped financial sanctions on companies helping to build Nord Stream 2, arguing that the pipeline rewards Russia and deepens Europe’s reliance on Russian gas. In large part because it has no effect on their constituents, Nord Stream 2 is a rare bipartisan issue among members of Congress. Imposing sanctions allows American legislators to sound tough on Mr. Putin at little cost.

Underneath the heated assertions and veiled threats lies the mundane reality that Russia’s ability to use gas as a tool of political pressure is already much diminished — something the completion of Nord Stream 2 would do little to change. But canceling the project as punishment for Mr. Navalny’s treatment is unlikely to achieve much, either. He is clearly a threat the Kremlin wishes to vanquish, at some cost.

The clamor over Nord Stream 2 shows, more than anything, a simple truth: When it comes to dealing with Russia, there are very few good options.