“He’s entering very dangerous territory!” Trump said after former Russian President Dmitry Medvedev mocked him online.

Dmitry Medvedev in tit-for-tat war of words with US president over ceasefire and nuclear threats

The former Russian president Dmitri Medvedev offers President Trump a useful foil to criticize without rebuking Vladimir Putin, one analyst said.

“He’s entering very dangerous territory!” Trump said after former Russian President Dmitry Medvedev mocked him online.

Trump escalates his war of words with Dmitry Medvedev, who had recently warned that U.S. actions were driving the country toward direct conflict with Russia