Heads of state and government are typically called Mr. President or Madam Prime Minister. So when President Donald Trump used a post Thursday on his social media site to speak directly to Russia's president,

President Trump, who just hours earlier had suggested that Ukraine’s president was the central impediment to peace, issued a rare public rebuke of Vladimir Putin: “Vladimir, STOP!” Trump wrote on his social media platform.

US President Donald Trump said he is “not happy” after Russia launched its deadliest wave of attacks on Kyiv in nine months, telling President Vladimir Putin to “STOP!” as he attempts to push Ukraine to agree on a contentious ceasefire proposal.