KYIV (Reuters) – Russian President Vladimir Putin is holding a gun to Ukraine’s head in an effort to force a change to the architecture of European security, British Prime Minister Boris Johnson said on Tuesday, stressing he was not exaggerating Russia’s threat. “This is a clear and present danger. We see large numbers of troops massing, we see preparations for all kinds of operations that are consistent with an imminent military campaign,” Johnson said, adding he would talk to Putin on Wednesday. “It’s about the whole European security architecture, because be in no doubt about what I think P…