Representative Elise Stefanik is a member of President Trump’s defense team.  In this interview the issue of the deficient articles is raised surrounding witnesses.
House witnesses who gave testimony when the articles were framed could be considered appropriate, if needed, when debating those articles in the Senate.  However, witnesses not called by the House; and therefore not used in the assembly of the articles being debated in the Senate; are not valid for consideration.

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It is not the responsibility of the Senate, nor is it constitutionally valid, for the Senate to attempt to rehabilitate improperly constructed articles simply because the House refused to assemble with due diligence.  Any evidence, including witnesses, that falls outside the originating assembly of the two House articles should be considered null and void.