How Impeachment Proceedings Would Strengthen Congress’s Investigatory Powers - Just Security

Michael Stern -  a former counsel
to the U.S. House of Representatives
Nancy Pelosi and the House Democratic leadership should heed this well stated - and quite conventional - analysis by a former Senior Counsel to the House! Stern lays out a basic proposition: there is no font of power deeper than the House's exclusive power to define and charge an officer of the United States with a "high crime and misdemeanor".  The United States Supreme Court, like the Senate as both are currently constituted, is presumptively strongly inclined to protect the President.  The oversight and law-making power cannot, in this array, be counted on as sufficient to support the subpoenae and other investigatory steps the House has begun. - gwc
How Impeachment Proceedings Would Strengthen Congress’s Investigatory Powers - Just Security: By Michael Stern [former Senior Counsel to the U.S. House of Representatives (1996-2004)]

***Finally, initiating an impeachment inquiry provides the House with several “self-help” options to better secure the production of information. First, to the extent the House wishes to employ the remedy of inherent contempt (in which the House through its own agents would detain or fine a contumacious witness), this strategy would be most defensible in an impeachment proceeding where the House is exercising a judicial function. 

Second, if President Trump continues to defy or direct others to defy congressional subpoenas especially for appearance before an impeachment hearing, this in itself could support an article of impeachment. Third, the House could draw an adverse inference from the unjustifiable failure to produce evidence, finding that the president’s refusal to provide information reflects the fact that it would not be helpful to his case.

In short, initiating a formal impeachment proceeding, though not a silver bullet, would significantly enhance the House’s ability to gather relevant information in a timely fashion. Claims that oversight hearings are equally powerful are just wishful thinking.