After all the speculation of the past few months, EU leaders finally decided on August 30 to appoint Donald Tusk, Poland’s prime minister, as president of the European Council, the body that represents national governments. Federica Mogherini, Italy’s foreign minister, will become the EU’s new foreign policy chief. If, unlike their predecessors, the two appointees are given full rein to shape EU strategy, these could be crucial positions.

With the Ukraine crisis and the conflicts in Europe’s fragile Southern neighborhood deteriorating ever further, the EU is more than ever in need of strong and decisive leadership in Brussels.

Of course, the world won’t wait until Mogherini and Tusk take office in November and December respectively. In Ukraine, Russian President Vladimir Putin, intent on setting the agenda for that country, has already stepped up his incursion.

Judy Dempsey Dempsey is a nonresident senior fellow at Carnegie Europe and editor in chief of Strategic Europe. More > @Judy_Dempsey

On August 28, NATO revealed satellite pictures of Russian troops operating deep inside Ukraine, confirming reports from other sources of an invasion. Three days later, Putin proposed the idea of statehood for eastern Ukraine, a euphemism for breaking up the country. Clearly, Western sanctions against Russia haven’t impressed Putin much so far.

Yet at their summit on August 30, EU heads of state and government procrastinated again, saying they would consider imposing another batch of sanctions in a week’s time. The leaders asked the European Commission to look into the matter.

The governments of countries such as Austria, Cyprus, the Czech Republic, Hungary, and Slovakia want to avoid a conflict with Russia at almost any price. Other leaders, such as German Chancellor Angela Merkel, still hope to offer Putin a face-saving exit. Yet if Merkel gives Putin a way out at the expense of Ukraine’s desire to integrate more with the West, the rest of Europe will suffer untold consequences.

Beyond the Ukraine crisis, will Tusk and Mogherini be able to make a difference to the EU’s security and defense ambitions?

At the outset, Tusk’s appointment is good news. It is the first time a leader from “new” Europe has been given a top job, thanks to Merkel and British Prime Minister David Cameron, who backed the Polish premier’s nomination.

Leaving aside the fact that Tusk’s selection is good for the faltering Polish-German relationship, having a Pole in one of the EU’s top jobs serves as a useful demonstration to Putin. Tusk is already preparing himself for a disagreement with Mogherini, seen by many as softer toward Moscow, and some member states over whether to hold an EU-Russia summit in December.

Tusk, who with his foreign minister, Radek Sikorski, has fought hard for a much more credible EU foreign and security policy, must use his new post to achieve progress on that account. Tusk’s appointment could also be good news for revamping the EU’s Eastern Partnership, the policy that governs relations with the union’s Eastern neighbors and a main strategic interest of Poland, Sweden, and the Baltic states.

Another plus is that Tusk has vowed to try to keep Britain in the EU by promising some reforms. His liberal economic tendencies are attractive to Cameron. But while Tusk managed to keep Poland from sliding into recession—the only EU country to avoid such a fate during the euro crisis—his record in pushing through reforms at home has been disappointing, to say the least.

That aside, as an Atlanticist, Tusk could try to breathe some life back into negotiations over the proposed Transatlantic Trade and Investment Partnership.

Success in all of the above ultimately depends not on Brussels but on the member states. But if Tusk wants to have an impact, he will need to be his own man as far as possible. He will have to speak out clearly about his strategy for the EU and work hard with the member states.

At walking distance from Tusk’s future office in Brussels is the headquarters of the European External Action Service (what an ungainly name). There, Federica Mogherini will have to prove her credentials—and quickly.

Her acceptance speech on becoming the EU’s high representative for foreign affairs and security policy revealed little. Of course, she didn’t want to offend anyone, particularly not the Nordics, Balts, and Poles, who are skeptical about her attitude toward Putin. They remember that Mogherini’s first foreign visit during Italy’s last turn at the EU’s rotating presidency was to Russia.

Mogherini’s new job is a minefield. She will have to manage the diplomatic corps of the European External Action Service, an institution that still lacks a clear strategy for how it will fit in with the diplomatic services of the EU’s member states.

At the same time, Mogherini will serve as vice president of the European Commission, where she will have to cope with much infighting and egos. And she will have to deal with the big member states. Just as Tusk, a conservative, is beholden to Merkel and Cameron, the left-leaning Mogherini is beholden to French President François Hollande and other left-wing leaders.

Yet given all the calculations that went into these appointments, it is important to remember that Jean-Claude Juncker, the new president of the European Commission, is an integrationist to the bone. Tusk is too. Mogherini has no choice but to follow suit.

Indeed, the crises in Europe’s Eastern and Southern neighborhoods only confirm that the EU urgently needs a strong security, defense, and foreign policy that also addresses questions of EU enlargement and refugees.

Juncker, Tusk, and Mogherini face a great challenge. The conflicts that are shaking Europe’s neighborhoods mean that the temptation to turn the EU into a fortress is bigger than ever. The three leaders must work together to forge a consensus with the member states on an open EU ready to defend and extend its values of human rights, freedom, and opportunity.