Russia's opposition supporters carry portraits of slain Kremlin critic Boris Nemtsov during a march in Moscow last year. (Yuri Kadobnov/Agence France-Presse via Getty Images)

Ellen Bork is senior fellow at the Foreign Policy Initiative and visiting fellow at the Henry Jackson Society. David J. Kramer is senior director for human rights and democracy at the McCain Institute.

Members of Russia’s democratic opposition will march through Moscow on Saturday in memory of Boris Nemtsov on the first anniversary of his assassination. Nemtsov, a former deputy prime minister and co-leader of the opposition party Parnas, was shot in the back on a bridge just steps from the Kremlin.

The tribute to Nemtsov comes amid escalating threats against his colleagues in the democratic movement. Over the past three weeks, Mikhail Kasyanov, a former prime minister and surviving chairman of Parnas, has received death threats, been assaulted in a Moscow restaurant and had his campaign for the Duma elections in September physically disrupted.

Whether Russian President Vladi­mir Putin is behind the targeting of his critics or simply tolerates it, it’s time for the Obama administration to break its silence on threats to the democratic opposition and put serious pressure on Putin to stop them.

The menacing harassment of Kasyanov follows a familiar and disturbing pattern. On Jan. 31, Ramzan Kadyrov, the Kremlin-appointed Chechen strongman, posted an Instagram video of Kasyanov, showing him in the crosshairs of a rifle. The caption read: “Whoever doesn’t get it will get it!” — an apparent reference to Nemtsov’s murder. It might also have referred to Vladimir Kara-Murza, another democratic opposition leader also pictured in the video, who survived a nearly fatal poisoning in Moscow in May. In January, Kadyrov ratcheted up the propaganda war against the democratic opposition, calling them “traitors” who should be locked up in psychiatric wards, a threat that carries echoes of Soviet-era repression.

Before Nemtsov was killed, Kremlin-sponsored propaganda painted him as a “traitor” intent on “swallowing, strangling and dismembering Russia.” He was taunted by stunts such as having a net thrown over his head or being photo-bombed by transvestites. On Feb. 9, Kasyanov was assaulted in a Moscow restaurant by a group of men who made threats and smeared cake on him. Another opposition leader, Aleksei Navalny , was hit with cake on Thursday by two men as he entered the office of his anti-corruption foundation. In today’s Russia, such things are not mere pranks but potential precursors to more serious harm.

Whether Kadyrov is acting at the direction of the Kremlin remains murky, but two things are clear. Kadyrov is a Putin acolyte. “We will gladly fulfill any order, in any spot in the world where our president tells us to go,” he told a crowd of supporters in December 2014. And Putin has neither reined in Kadyrov nor distanced the Kremlin from the Chechen strongman. To the contrary, shortly after Nemtsov was killed, Putin gave Kadyrov a presidential award despite the fact that (or because) one of the killers had served in a military force under Kadyrov’s command. A report released this week in Moscow, “Threat to National Security,” by another democratic opposition leader, Ilya Yashin, paints Kadyrov as “a threat to Russia’s national security.”

But Kadyrov isn’t the only problem. On Feb. 12, Kasyanov cut short a campaign stop in Nizhny Novgorod after police allowed provocateurs to disrupt a meeting with local democracy activists, with more violence threatened for the next day. Regional officials told the media not to cover Kasyanov’s appearances.

Kasyanov plans to return to the campaign trail after the Nemtsov anniversary march. So far, however, the Obama administration has not responded to the recent threats against the democratic opposition. Just as troubling is its grudging, circumscribed implementation of the Magnitsky Act, the primary vehicle for exerting leverage on Putin over respect for individual rights in Russia. The most recent additions to the Magnitsky sanctions list were five low-level Russian officials. No senior Russian officials or members of Putin’s inner circle have been publicly sanctioned under the act, which imposes a U.S. visa ban and asset freeze on Russian officials involved in gross human rights abuses. Nor has Kadyrov, at least publicly, despite the State Department’s assessment that he rules Chechnya through tactics including extra-judicial killings, torture and rape; media reports state that he has been listed on a classified version of the act.

At the same time, the Obama administration has told the BBC that Putin is “the picture of corruption.” For “many, many years,” Adam Szubin, acting undersecretary of the Treasury for terrorism and financial intelligence, told BBC Panorama, “we’ve seen him enriching his friends, his close allies, and marginalizing those who he doesn’t view as friends using state assets.” Yet the administration has refrained from sanctioning Putin himself; instead it stubbornly pursues strategic cooperation on Syria, even as Russian airstrikes continue to kill civilians, drive up the flow of refugees and prop up Syrian dictator Bashar al-Assad.

The United States is not alone in this approach. British Prime Minister David Cameron has announced that he will keep calm and carry on with relations with Moscow despite the conclusion of an inquiry in January that Putin “probably” approved the murder of former spy Alexander Litvinenko in a London hotel.

All of this adds up to an alarming situation for the Russian democracy movement. Barring stronger pushback from the West, there will be more threats and, we fear, worse for Kasyanov and his colleagues. It’s happened before. We must not let it happen again.