Impeachment in the United States - Wikipedia
"When the Supreme Court has considered similar issues, it held that the power to secure "needed information ... has long been treated as an attribute of the power to legislate. ... [The power to investigate is deeply rooted in the nation's history:] It was so regarded in the British Parliament and in the colonial Legislatures before the American Revolution, and a like view has prevailed and been carried into effect in both houses of Congress and in most of the state Legislatures."
McGrain v. Daugherty, 273 U.S. 135, 161 (1927). The Supreme Court also held, "There can be no doubt as to the power of Congress, by itself or through its committees, to investigate matters and conditions relating to contemplated legislation."
Quinn v. United States, 349 U.S. 155, 160 (1955).
The Supreme Court has also explained that Congress has not only the power, but the duty, to investigate so it can inform the public of the operations of government:
It is the proper duty of a representative body to look diligently into every affair of government and to talk much about what it sees. It is meant to be the eyes and the voice, and to embody the wisdom and will of its constituents. Unless Congress have and use every means of acquainting itself with the acts and the disposition of the administrative agents of the government, the country must be helpless to learn how it is being served; and unless Congress both scrutinize these things and sift them by every form of discussion, the country must remain in embarrassing, crippling ignorance of the very affairs which it is most important that it should understand and direct. The informing function of Congress should be preferred even to its legislative function.
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Why do you fear Congress doing their duty by investigating the Executive branch?
Too much power has been ceded to the Executive branch, not just with Trump but with others as well ( yes Obama too).
Its time as a country to curb some of that power.
Thanks for the excuse Trump