(CNN) – For President Barack Obama, it seems there is no escape.
Even on his eight-hour trip to Mexico for a summit of North American leaders, the president was forced to switch gears to yet another world crisis. This time, he issued a stern warning on the violence in Ukraine.
"There will be consequences if people step over the line, and that includes making sure that the Ukrainian military does not step into what should be a set of issues that can be resolved by civilians," President Obama said.
President Obama's options for Ukraine are limited. The U.S. and European leaders are threatening the Ukrainian government with sanctions. But the administration has learned the diplomatic path can yield few results, and more bloodshed, as it has so far in Syria.
"When is the United States of America going to show some leadership? When is the president of the United States going to look at history and say, 'how is history going to judge me and this country,'" Sen. John McCain, R-AZ, said Wednesday.
An eerily similar to the situation in Syria, a key obstacle to the president's approach in Ukraine is Russian President Vladimir Putin.
"Putin needs to understand that Obama can be as tough as he is that the United States is not playing patty cake here. We do have vital interests in that region. We have interests in the human rights of people that live in that region of the world," CNN senior political analyst David Gergen said.
The president's constraints are also in display at Wednesday's North American summit.
Canada's prime minister is complaining he may have to wait for a new presidential administration to approve the contested Keystone XL pipeline.
Mexico wants to see progress on immigration reform in the U.S., something the president cannot deliver without Republican help.
Also on topic during the summit, President Obama's desire to expand authority from Congress to conduct new trade deals, but on that issue, it's his fellow Democrats who are saying no.
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