The countries will negotiate next week through intermediaries in Vienna to try to bring both back into compliance with the 2015 nuclear agreement.

Harvard Kennedy School (HKS) and the German Council on Foreign Relations (DGAP) convened a strategy group of experts and former government officials from the United States and Europe over the past year to discuss the crisis in the transatlantic relationship and to propose a strategy to revive and strengthen it.

The killing of Iran’s top nuclear scientist is likely to impede the country’s military ambitions. Its real purpose may have been to prevent the president-elect from resuming diplomacy with Tehran.

The secretary of state is preparing an argument that the U.S. remains a participant in the Obama-era nuclear deal, with the goal of extending an arms embargo or destroying the accord.

As accusations swirled Sunday about Russia’s efforts to interfere with the 2020 election, President Trump’s national security adviser and former Vice President Joseph R. Biden Jr. could not agree on what Moscow is, or is not, doing.

Their disagreement came as intelligence officials disputed reports that emerged last week about a briefing of the House Intelligence Committee. The officials now maintain that the House members either misheard or misinterpreted a key part of the briefing, and that the Office of the Director of National Intelligence did not mean to say that it believes the Russians are currently intervening in the election explicitly to help President Trump.

America’s global campaign to prevent its closest allies from using Huawei, the Chinese telecom giant, in the next generation of wireless networks has largely failed, with foreign leaders publicly rebuffing the United States argument that the firm poses an unmanageable security threat.

President Trump opened a small window for diplomacy with Iran on Wednesday, but combined his words with bald threats that made it hard to see how the two countries could break out of their cycle of confrontation and revenge.

Rudolph W. Giuliani, the former New York mayor at the center of the impeachment investigation into the conduct of Ukraine policy, makes a living selling cybersecurity advice through his companies. President Trump even named him the administration’s first informal “cybersecurity adviser.”

President Trump is pushing Boris Johnson, the incoming prime minister of Britain, toward a hard break with the European Union. But Mr. Johnson could be constrained.

President Trump and his aides have sent a dizzying, seemingly conflicting set of messages to Iran in recent weeks, ordering more troops to the Middle East and a carrier to the Arabian Sea as military threats even while declaring that Washington is seeking new negotiations, not war.