if it is an existential threat for our country, it can be used in accordance with our concept. >> joining me now is brian clause, professor of global politics at university college london. professor, great to have you on. it's part of russian doctrine, and we all thought it to mean if the russian homeland was invaded, part is the use of nuclear weapons. now, the perception, how has it changed? if we are talking about an existential threat to vladimir putin, what does he see as an existential threat now? . >> well, it's not very surprising they're not ruling out the use of nuclear weapons. we would expect that to be the case. and i think it's one of those areas where we have to understand russia's place in the world and how it is shifting very, very quickly. before this invasion, russia's economy was sandwiched between italy and mexico in terms of its size.