Ukraine's future could hinge on a hastily assembled meeting Monday at the White House as Ukrainian President Volodymyr Zelenskyy brings with him an extraordinary cadre of European leaders to show U.S. President Donald Trump a united front against Russia. The European political heavy-hitters were left out of Trump's summit with Russian President Vladimir Putin last Friday, and they look to safeguard Ukraine and the continent from any widening aggression from Moscow. The meeting also is a test of America’s relationship with its closest allies after the European Union and United Kingdom accepted Trump’s tariff hikes partly because they wanted his support on Ukraine.