Peter Baker for the NYT:

The emerging battle over the future of Mr. Trump’s presidency will explore as never before the scope and limits of a commander in chief’s interactions with other countries. His adversaries echo the fears of the founders in accusing Mr. Trump of committing high crimes by pressuring Ukraine to dig up dirt on Democratic opponents while holding up American aid. Mr. Trump contends that impeaching him would infringe on the ability of future presidents to conduct foreign policy.

Unlike the impeachment battles involving Andrew Johnson, Richard M. Nixon and Bill Clinton, the debate over Mr. Trump turns on whether a president can solicit or accept help from abroad to advance his political fortunes and where lies the line between the national interest and personal interests.