The Democrats said in their letter to Pence that failure to comply will be evidence of obstruction of the House’s impeachment inquiry and “may be used as an adverse inference against you and the president.”
The chairmen of the House committees leading the investigation said they're investigating the extent to which Trump "jeopardized national security by pressing Ukraine to interfere with our 2020 election and by withholding security assistance provided by Congress to help Ukraine counter Russian aggression, as well as any efforts to cover up these matters."