Chicago - Hillary Clinton on Thursday took a swipe at Libertarian presidential candidate Gary Johnson, who further crippled his longshot bid for the White House by failing to name a single foreign leader he likes.Johnson, who has virtually no chance of making it to the White House, could still prove a thorn in the Democratic nominee's side by siphoning off votes in Colorado and other battleground states.In a cringe-inducing minute-long segment during a MSNBC town hall-style event, Johnson sat speechless after host Chris Matthews asked him, "Who's your favourite foreign leader? Any one of the continents, any country, name one foreign leader that you respect and look up to, anybody."The embarrassment follows another live television crash-and-burn, when the former New Mexico governor replied "what is Aleppo?" to an interview question about the Syrian city at the centre of global attention.Praises for MerkelAsked about her favourite world leader by campaign reporters in Chicago on Thursday, Clinton said "oh, let me think," before bursting into laughter."No, look," she continued. "I like a lot of the world leaders. One of my favourites is Angela Merkel." "I think she's been an extraordinary, strong leader during difficult times in Europe, which has obvious implications for the rest of the world.""Her leadership and steadiness on the euro crisis and her bravery in the face of the refugee crisis is something that I am impressed by."The two women have known each other for a long time, "back into the 1990s," Clinton boasted."I've spent a lot of time with her and I hope that I'll have the opportunity to work with her in the future," she added. "But we could talk about lots of different leaders if you want to sometime."Clinton's Republican rival Donald Trump, who has previously castigated Merkel, also decided to choose her as his favourite world leader on Thursday."I think Merkel is a really great world leader," he told New England Cable News before adding that he "was very disappointed" in her because of "the whole immigration thing."