BERLIN — Republican presidential contender Jeb Bush is warning Russia that if he becomes president, the U.S. will do more to tamp down Vladimir Putin’s aggression, especially in Ukraine and Eastern Europe, and to “isolate his corrupt leadership from his people.” But Bush did little to tip his hand on what those steps would be.

In his first foreign speech of the 2016 campaign, Bush criticized what he called dramatic declines in U.S. military spending, suggesting that has undercut credibility as Washington and its allies confront threats in Eastern Europe and elsewhere. Putin, he said, must know in advance that there will be consequences to his actions, because the Russian president “will push until someone pushes back.”

Bush was critical of what he termed a reactive approach to crisis in Eastern Europe by the Obama administration. But his prescriptions were largely along the lines of what the U.S. is already doing, primarily pushing economic sanctions on Russia and sending military and economic aid to Ukraine.

As for NATO military exercises being conducted in Eastern Europe, Bush agreed they were a useful signal to Moscow of the alliance’s determination. “I think we should probably do it more robustly,” he said.

The former Florida governor addressed a major economic conference in Berlin as part of a trip that precedes his planned announcement in Miami on Monday that he is running for the 2016 nomination. He’s also visiting Poland and Estonia.

Bush was given a prominent platform – the economic council of Chancellor Angela Merkel’s party, the Christian Democratic Union.

Many in the audience of 2,000 broke into applause when Bush invoked his father, George H.W. Bush, who was president when the Soviet Union collapsed, Eastern European nations turned to their own destiny and Germany reunited as the Berlin Wall dividing East and West came down. But he did not mention George W. Bush, who was unpopular in Western Europe when he left office, but had a solid relationship with Merkel.

“That reunification, as you all know, was not inevitable,” Bush said. “Many leaders doubted. Many of the people even in this country doubted. Many people in the United States as well doubted whether it should be attempted.” But due to Chancellor Helmut Kohl’s determination and with the elder Bush’s support, he said, “Germany is whole and Germany is free.”

Without many specifics, Bush called for deeper economic and security ties with eastern European nations vulnerable to Russian meddling.

“Russia must respect the sovereignty of all of its neighbors,” Bush said.

But as NATO confronts crisis, he said, it must do so in a way that does not push Russia away for another generation.