Document ID: ./input/supremecourt_opinions/opinions/19pdf/19-715_febh.pdf
Page Number: 39.0

14 

TRUMP v. MAZARS USA, LLP 

THOMAS, J., dissenting 

cussion  strongly  suggests  the  subpoena  was  unconstitu-
tional.4 

The Court instead based its decision on the fact that the 
subpoena at issue “ma[de] inquiry into the private affairs of 
the citizen.”  Id., at 190.  Such a power, the Court reasoned,
“is judicial and not legislative,” id., at 193, and “no judicial 
power is vested in the Congress or either branch of it, save 
in the cases” of punishing Members, compelling Members’ 
attendance,  judging  elections  and  qualifications,  and  im-
peachment and trial, id.,  at 192–193.  Notably, the Court
found no indication that the House “avowed to impeach the 
secretary,” or else “the whole aspect of the case would have
been changed.”  Id., at 193.  Even though the Court decided 
Kilbourn  narrowly,  it  clearly  entertained  substantial
doubts about the constitutionality of legislative subpoenas
for private documents. 

D 

Nearly half a century later, in McGrain v. Daugherty, the 
Court reached the question reserved in Kilbourn—whether 
Congress has the power to issue legislative subpoenas.  It 
rejected Kilbourn’s reasoning and upheld the power to issue
legislative subpoenas as long as they were relevant to a leg-
islative power.  Although McGrain involved oral testimony,
the Court has since extended this test to subpoenas for pri-
vate documents.  The Committees rely on McGrain, but this 
line of cases misunderstands both the original meaning of 
Article I and the historical practice underlying it. 

—————— 

4  According to Justice Miller’s private letters, “a majority of the Court, 
including Miller himself, were of the opinion that neither House nor Sen-
ate had power to punish for contempt witnesses who refused to testify 
before investigating committees.”  T. Taylor, Grand Inquest: The Story 
of Congressional Investigations 49 (1955).  Only Justice Miller’s desire
to “ ‘decid[e] no more than is necessary’ ” caused the Court to avoid the 
broader question.  Ibid.