President Obama may be considering sending weapons to Ukraine to help its soldiers repel Russian-backed separatists, but he isn't drawing a "red line" on what would prompt him to do so. The subject of a red line in foreign policy is, of course, an uncomfortable one for the president, who infamously ignored the bright demarcation he set when the Syrian army was caught using chemical weapons against rebels in 2013.

During a press conference Monday with German Chancellor Angela Merkel, Obama made clear that sending defensive arms to Ukraine was one of the options his team was mulling if neither diplomacy nor economic sanctions persuades Vladimir Putin to leave Ukraine alone. That would undoubtedly represent a significant escalation of U.S. involvement in the conflict, and when asked by a German reporter about a "red line," Obama said no. "There's not going to be any specific point at which I say, 'ah, you know, clearly lethal defensive weapons would be appropriate here,'" the president replied. "It is our ongoing analysis of what can we do to dissuade Russia from encroaching further and further on Ukrainian territory."

The exchange was notable because of the presence of Merkel, who during a speech on Saturday explicitly rejected the possibility of sending arms to Ukraine on the grounds that it would make the situation worse, and that winning a military conflict with Russia was impossible. She stuck to that position Monday at the White House, even as Obama refused to rule it out. (Merkel said she wanted to make at least one more attempt to broker a ceasefire in the region.) The president is also facing increasing pressure domestically to bolster assistance to Ukraine, and his nominee for defense secretary, Ashton Carter, told a Senate committee last week that he was "very much inclined" toward arming Ukraine.