President Obama welcomed Ukraine's interim Prime Minister Arseny Yatsenyuk to the White House on Wednesday, in a show of solidarity.
"My hope is that as a consequence of diplomatic efforts over the next several days, that there will be a re-thinking of the process that's been put forward," said Mr. Obama.
Yatsenyuk said he would welcome direct talks with Moscow.
"My message to President Putin: Mr. Putin, tear down this wall, the wall of war, intimidation, and military aggression," said Yatsenyuk, urging the Russian leader to drop his flat refusal to recognize the new Ukrainian government or hold any discussion with its representatives.
Yatsenyuk said he fears Putin might try to take control of more territory in eastern Ukraine, where many people favour ties with the Kremlin over Europe.
If that were to happen, Kerry told lawmakers on Wednesday, it would trigger extremely punishing sanctions against Russia.
"It can get ugly fast if the wrong choices are made," said Kerry, "it can get ugly in multiple directions."
Yet another Foreign Policy disaster for the Obama administration.
Peace through strength, not perceived weakness.