War for Ukraine: The Hidden Meaning of 'Gird Your Loins' Speech?

I'm sure you guys have already heard about this speech...
blogs.abcnews.com...


Basically, while speaking before Obama supporters Biden said that within six months of ascending to the presidency that Obama would be 'tested' by foreign governments and that his supporters should stand by him even if he makes very unpopular decisions.

Now, I am all for politicians doing what they think is right, even if it is unpopular, but what sort of decision would be unpopular in regards to a diplomatic crisis wherein the US was challenged? In other words... it's easy to see how an aggressive move by the US would be considered unpopular by the public... but what sort of defensive decision would be considered unpopular by the public? In saying that Obama would be challenged Biden is essentially saying that the US would be challenged. One would expect most Americans, no matter their party, to rally behind the country if it was challenged. Does this blurb imply that Obama would do something defensively that will be unpopular?

A likely scenario where America is challenged is one where Russia invades the Ukraine. Would the unpopular decision be one where Obama conceded eastern Europe to the Russians? Or would standing up to the Russians just be unpopular among liberals?