What does Boris Johnson believe is necessary for effectively deterring Russian aggression against Ukraine?

Boris Johnson emphasizes that a US security guarantee is essential for effectively deterring Russia from attacking Ukraine again. While he indicates willingness to consider committing British forces on the ground alongside other nations if there is a lasting peace agreement, he stresses that this European effort must be backed by American support. Johnson specifically states that 'a US Backstop' is necessary because only a US Security guarantee can provide the level of deterrence needed against Russian aggression. This highlights his view that European security efforts, even with British participation, require American backing to be truly effective in protecting Ukraine from future Russian threats.