WASHINGTON (AP) — How do American leaders and their allies intend to respond if President Vladimir Putin seeks to escalate his way out of a bad situation on Ukraine’s battlefields, and makes good on renewed threats of annexing territory or even using nuclear weapons? At least to start with, by trying to double down on the same tactics that have helped put Russia in a corner in Ukraine, U.S. and European leaders have made clear: more financial penalties and international isolation for Russia, more arms and other backing for Ukraine. That won't necessarily be easy. It's been tough enough staying...