At the same time murderers were attacking Paris, the West’s top diplomats were traveling to Vienna with the goal of replacing a mass murderer, Syrian President Bashar Assad. The world’s attention is now on the Islamic State, taking the pressure off the Syrian regime right at the moment when pressure might have been effective.

The Syrian regime has avoided large-scale fights with the Islamic State. Assad wants the Islamic State to remain an imminent threat, so the international community will see two options: keep Assad or let terrorists take over Syria. Assad created the chaos that allowed the Islamic State to rise. His regime now has a strategy that bolsters the Islamic State’s hold on northern Syria: The U.S.-backed Syrian rebels who are supposed to be fighting the Islamic State are being slaughtered by the Syrian Army and by Assad’s Iranian and Russian allies. Assad’s brutal campaign against Sunni communities drives thousands of young Syrians to join the jihadis.

And now that the Islamic State has pulled off a series of devastating attacks in Paris, Western governments are promising a “ruthless,” “merciless,” “pitiless” war against the group. But none are mentioning Assad.

Secretary of State John Kerry said Saturday what most Syrian opposition figures say repeatedly to anyone who will listen: Assad is the magnet for the terrorists, and Syria will never be free from terror until Assad is out of power. Kerry wants him to step down.

“I hope it will happen. I pray it will happen. Because if it doesn’t happen, this war won’t end. This war can’t end as long as Bashar Assad is there,” Kerry said in Vienna when announcing small progress in the multinational talks to start a Syrian peace process.

Kerry pointed out that over 300,000 have died in Syria, the vast majority at the hands of the Assad regime. He mentioned the barrel bombs, the torture of civilians in custody, the use of chemical weapons, all by Assad’s forces. Only if Assad steps aside can the world join together to fight against the Islamic State, he said.

Russian Foreign Minister Sergei Lavrov was sitting next to Kerry and was quick to disagree. Following the Russian government line, Lavrov pointed out that the U.S. led the drives to topple Saddam Hussein in Iraq and Moammar Gadhafi in Libya, leading to growing terrorism in both countries. He then argued that the Paris attacks point to a need to keep Assad in power.

“The Paris attacks have shown, alongside with ISIS claiming responsibility for it, that it doesn’t matter if you are for Assad or against him; ISIS is your enemy. So it’s not about Assad,” Lavrov said.

Assad himself tried to spin the Paris attacks into a justification for the international community to support his government. France has long been a supporter of the Syrian opposition, a policy Assad says has encouraged terrorism.

“The question that is being asked throughout France today is, was France’s policy over the past five years the right one? The answer is no,” Assad said Saturday.

Looking at the reactions of top U.S. officials and candidates in both parties Saturday, it appears that Lavrov’s preference, to focus on the Islamic State and not Assad, is winning out. The New York Times reported the Paris attacks may lead to a more aggressive U.S. war against the group. Commentators predict the American public will now wholeheartedly support that action. Some are calling for the U.S. to “roll on Raqqa,” the caliphate’s capital.

“The question of whether President Assad needs to go or whether he is part of the solution here, we need to look at again,” former CIA Deputy Director Mike Morrell said on “Face The Nation” on Sunday morning, arguing for cooperating with the Syrian Army against the Islamic State. “Clearly he’s part of the problem, but he may also be part of the solution.”

Former White House official Dennis Ross tweeted a response: “Bashar Assad is not the answer to defeating ISIS; he helped produce them, buys their oil, is the cause that draws foreign fighters to them.”

At Saturday night’s Democratic debate, each candidate promised to fight the Islamic State, but none mentioned Assad. Even Republican candidates who have been staunch advocates of arming the rebels fighting Assad, such as Sen. Marco Rubio, focused their reactions to the Paris attacks on the Islamic State instead.

“The attacks in Paris are a wake-up call. A wake-up call to the fact that what we’re involved in now is a civilizational conflict with radical Islam,” Rubio said in a statement.

Some experts warn that even if you completely destroy the Islamic State in Syria and Iraq, if Assad is allowed to continue his campaign of terror, another ruthless organization will just appear and take its place. That’s why Kerry’s drive to replace Assad, despite a low chance of success, is crucial.

“Making sure Assad is not the answer is key to a viable settlement,” said Andrew Tabler, senior fellow at the Washington Institute for Near East Policy. “At the end of this process, it has to be a viable agreement that puts a country back together or we are going to have terror attacks in the U.S.”

World powers can avenge this week’s tragedy by killing members of the Islamic State. But if the goal is to destroy the Islamic State for good — as President Barack Obama says — then the campaign must be matched by a renewed push to oust Assad. There is a lot of temptation, in the wake of the horror in Paris, to treat only the symptoms of instability in Syria. But the Assad regime is the disease, and the symptoms will not go away until Assad is gone.

By Josh Rogin

Josh Rogin is a Bloomberg View columnist who writes about national security and foreign affairs. — Ed.