The Treasury Department’s deputy secretary, Wally Adeyemo, has been leading the effort to crack down on evasion and to coordinate with Europe.WASHINGTON — When Russia imposed retaliatory sanctions on top American officials last month, its government targeted President Biden and his top national security advisers, along with Wally Adeyemo, the deputy Treasury secretary, whose agency has been crafting the punitive measures aimed at crippling Russia’s economy.Russia’s move, while wholly symbolic, underscored the central role that the Treasury Department has been playing in designing and enforcing the most expansive financial restrictions that the United States has ever imposed on a major economic power.Those restrictions amount to an economic war against Russia, which is entering a critical phase as the toll of fighting in Ukraine continues to escalate and as the Russian government tries to find ways to evade or mitigate fallout from Western sanctions.In an attempt to prevent Russia from skirting the penalties, Mr. Adeyemo, a 40-year-old former Obama administration official, spent last week crisscrossing Europe to coordinate a crackdown on Russia’s evasion tactics and to plot future sanctions. In meetings with counterparts, Mr. Adeyemo discussed plans by European governments to target the supply chains of Russian defense companies, some of which the U.S. placed under sanctions last week, and he talked about ways the United States could help provide more energy to Europe so European countries could scale back purchases of Russian oil and gas, a Treasury official said.On Wednesday, five days after Mr. Adeyemo returned, the Biden administration announced additional sanctions on Russian banks, state-owned enterprises and the adult daughters of President Vladimir V. Putin.Still, it remains to be seen whether the sweeping penalties aimed at neutering Russia’s economic power are working.Over the past six weeks, the United States and its allies in Europe and Asia have imposed sanctions on large financial institutions in Russia, its central bank, its military-industrial supply chain and Mr. Putin’s allies, seizing their yachts and planes. Imports of Russian oil to the United States have been banned, and Europe is developing plans to wean itself off Russian gas and coal, albeit slowly. This week, the Treasury Department prohibited Russia from making sovereign debt payments with dollars held at American banks, potentially pushing Russia toward its first foreign currency debt default in a century.But thus far Russia has kept paying its debts. Currency controls imposed by Mr. Putin’s central bank, which restricted Russians from using rubles to buy dollars or other hard currencies, along with continuing energy exports to Europe and elsewhere have allowed the ruble to stabilize and are replenishing Russia’s coffers with more dollars and euros. That has raised questions about whether the measures have been effective.“I think we’re grappling with the aftershocks of the shock and awe of the sanctions that were put in place and the recognition that sanctions take time to fully impact an economy,” said Juan C. Zarate, a former assistant secretary of the Treasury for terrorist financing and financial crimes. “It’s asking too much of sanctions to actually turn back the tanks, especially when sanctions have been implemented after the invasion.”At a speech in London last week, Mr. Adeyemo promoted the ability of sanctions to change behavior, describing the measures as a part of the equation that adversaries such as Russia need to consider when they violate international norms.“The idea that you can violate the sovereignty of another country and enjoy the privileges of integration into the global economy is one our allies and partners will not tolerate,” Mr. Adeyemo said at Chatham House, a think tank.Yet even the United States, which is not reliant on Russian energy, has wrestled with how far to go with its penalties.Within the Treasury Department, officials have been in a debate about how far to push the sanctions without creating unintended consequences that would rattle the financial system and inflame inflation, which is soaring across much of the world.The impact on the U.S. economy has been a top priority, and Janet L. Yellen, the Treasury secretary, has expressed concern about measures that would amplify inflation. The sanctions on Russia have already led to higher prices for gasoline, and officials are wary that they could bring spikes in food and car prices as Russian wheat and mineral exports are disrupted.“Our goal from the outset has been to impose maximum pain on Russia, while to the best of our ability shielding the United States and our partners from undue economic harm,” Ms. Yellen told lawmakers on Wednesday.As officials considered how to target the ruble, Ms. Yellen, a former Federal Reserve chair, argued against just imposing a ban on foreign exchange transactions, which would prevent Russia from buying dollars. She suggested instead that immobilizing Russia’s foreign reserves — savings that are held in U.S. dollars, euros and other liquid assets — while creating exemptions for Russia to accept payment for certain energy transactions would be the most effective way to inflict pain on Russia’s economy while minimizing the impact on the United States and its allies.At a congressional hearing this week, Republicans criticized those carve-outs for being giant loopholes that allow Russia to earn hundreds of millions of dollars per day through oil and gas sales.Treasury Department officials have been tracking measures that Russia has been using to prop up its economy, such as buying stocks and bonds, and monitoring signs of a growing black market for rubles, which indicates the currency’s actual diminished value. The Biden administration has watched with concern as the value of the ruble has rebounded in recent weeks, undercutting pronouncements made by Mr. Biden that sanctions reduced the Russian currency to “rubble.”“Of course that means that, having said that, when the ruble rebounds for reasons that do not necessarily indicate weakness of sanctions, people will say, ‘Well, see, they failed,’” said Daniel Fried, a former U.S. ambassador to Poland and assistant secretary of state for Europe.A Treasury official said the United States was also keeping a private list of oligarchs whose financial transactions were under surveillance in preparation for sanctions so they could gain a better understanding of the networks of people that helped those individuals conceal their money. The United States has yet to impose sanctions on Roman Abramovich, a Russian billionaire who is already subject to European Union sanctions.Economists at the Institute of International Finance wrote in a research note this week that Russia’s domestic markets appeared to be stabilizing as a result of tight monetary policy, severe capital controls and its current account surplus.Russia-Ukraine War: Key DevelopmentsCard 1 of 4Missile attack. More