WASHINGTON — President Trump will have just wrapped up the first day of his summit meeting in Vietnam with Kim Jong-un, the North Korean leader, when back home in Washington, Michael D. Cohen, his former lawyer and fixer, takes the stand on Wednesday morning to testify publicly against him before the House Oversight Committee.

Two nearly simultaneous events and two very different story lines for Mr. Trump. One involves a leader he has assiduously courted and hopes will provide him with, at the minimum, an example of his ability to make peace with the United States’ adversaries. The other involves a former associate who has already detailed the president’s secrets to the special counsel and now will share some of them with the American public.

The clashing narratives follow what has become a frustrating pattern for Mr. Trump in which some of his biggest moments on the international stage have been overtaken by events at home. Foreign trips mark critical moments for every president. But for a president in search of evidence to support his claims that he has strengthened the United States’ position in the world, they have not always been the successes he had hoped to portray.

From his first foreign trip as president — to Saudi Arabia in 2017 — to his meeting last summer with Queen Elizabeth II, Mr. Trump has often found himself competing for coverage with some new and dramatic turn in the scandals that have consumed his administration.