evidence: Secretary of State Antony Blinken arrived in Kyiv on Tuesday in an unannounced diplomatic mission to reassure Ukraine that it has American support as it struggles to defend against increasingly intense Russian attacks. "We know this is a challenging time," Blinken said in the Ukrainian capital where he met with President Volodymyr Zelenskyy. [...] Blinken will "send a strong signal of reassurance" to Ukrainian leaders and civil society figures he will meet during his two-day visit, said the official, who spoke to reporters on condition of anonymity ahead of Blinken’s meetings.