Well, it was Trump's fault because he (somehow) lost the election, and nobody respects or fears Biden, thus they don't respect or fear the US, and feel emboldened to make aggressive territorial acquisitions, first Putin with Ukraine, and now China with Taiwan.
I fully expect North Korea to start making advances on South Korea at any point, despite the peace treaty Trump got them to sign.
Biden is a communist leader's dream American president. And while yes, /officially/ Putin isn't the leader of a communist country, everyone knows he's always been trying to revive the USSR. He's a democratic leader in name only.