Russia is stepping up its bombing campaign against Ukraine. So for weeks, Ukraine’s President Volodymyr Zelensky has been making a desperate plea to the United States and its NATO allies to impose a “no-fly zone” over the country — to keep Russian warplanes out of the sky. But a no-fly zone hinges on the notion that if a Russian plane violates the terms, it will be shot down. And the idea of entering into armed combat with a nuclear power is a clear and potentially catastrophic risk for Western leaders. This week, Zelensky is planning a virtual address to Canada’s House of Commons and the U.S. Congress, in the hopes of winning more support in his country’s fight against Putin’s military. Today on Front Burner, we speak to University of British Columbia’s Allen Sens about the case for and against a “no-fly zone,” whether there’s a red line in this war, and the ways in which it could escalate.