(CNN)Joe Biden and Donald Trump are locked in an extraordinary and escalating clash that has profound political consequences now and into 2024.

Biden took the showdown, which was triggered by the fallout over the US Capitol insurrection, up another notch on Monday by refusing to assert executive privilege over a second batch of documents that Trump wants to prevent the National Archives from turning over to the House select committing probing the January 6 attack. The development was first reported by CNN.

There have been occasions in US history when former presidents have sniped at and tried to undermine their successors. Many presidents have expressed private frustration with the antics of their predecessors. But nothing in the modern era matches the confrontation between the 45th and 46th Presidents.