President Barack Obama will this week head to the NATO summit in Wales, hoping to persuade more nations to join America in the fight against ISIS amid criticism that he has not acted forcefully enough against the terror group.

The well-funded, hyper-violent and media-savvy brand of militant Islam has attracted hundreds of members from Europe and Americas and stoked fears of an attack on Western targets. The meeting of NATO leaders, which formally begins Thursday, gives the president an opportunity to build support for continued airstrikes against ISIS fighters in Iraq and to get help curtailing the flow of money and weapons to the Sunni fighters.

There is less clarity on Obama’s approach in civil war-torn Syria, where ISIS is growing in power. “We don’t have a strategy yet," Obama admitted on Thursday. Since then, a chorus of bipartisan critics has urged him to stop deliberating and take bolder action. On Sunday Senate Intelligence Committee Chair Dianne Feinstein, a Democrat, said on NBC’s “Meet the Press” that Obama was being “too cautious” with Syria.

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Republicans have leveled even harsher criticism. Rep. Mike Rogers of Michigan said on “Fox News Sunday” that the president’s foreign policy was “in absolute free-fall.” Sens. John McCain and Lindsey Graham wrote earlier on Friday in the New York Times that the ISIS threat demands “a far greater sense of urgency.”

But airstrikes in Syria could be much riskier: America knows less about ISIS strongholds in the region, raising the potential for civilian casualties. “If they really want to destroy the Islamic State and stop them from being a threat, they are going to have to get a lot more committed,” Hayat Ailvi, professor of Middle East Studies at the U.S. Naval War College, told Reuters.

Obama plans to arrive in Wales early on Wednesday, when he’ll meet with NATO leaders on ISIS, administration officials have said. Ahead of the meeting, Germany and Australia announced Sunday that they would send weapons to arm Kurdish fighters who are trying to hold off ISIS advances in northern Iraq.

Opposing ISIS has made bedfellows of many countries who are otherwise at odds. The U.S., for example, has found itself on the same side of the conflict as Russia, Syria and Iran. Bringing these traditional opponents together for this cause could be a test of Obama’s diplomatic skills.

“It has to be patched together, somewhat ad hoc, with maybe some sort of informal and even clandestine agreement on who does what,” former U.S. national security adviser Zbigniew Brzezinski told the Wall Street Journal.

Secretary of State John Kerry plans to go to Wales with Defense Secretary Chuck Hagel to help build the coalition. Then they’ll go to the Middle East “to develop more support for the coalition among the countries that are most directly threatened,” Kerry wrote in the New York Times.

Kerry also pointed out that the U.S. will hold the presidency of the United Nations Security Council in September. “We will use that opportunity to continue to build a broad coalition and highlight the danger posed by foreign terrorist fighters, including those who have joined ISIS.”