Ukrainian President Volodymyr Zelensky was set to appeal directly to US senators for more support Tuesday ahead of a showdown over funding the war with Russia -- with the besieged US ally fast exhausting the aid Congress has approved so far.The cash has been held up for weeks by a row over domestic policy in Congress, as the White House has warned that existing funds will run out by the end of the year and that Russia's President Vladimir Putin could win the war if lawmakers fail to act.