Congressman Waxman wrote a letter to an Executive Branch employee:

"Congress has a constitutional duty to conduct oversight of the executive branch."

Doing one's duty means keeping all options on the table to defend the Constitution. Waxman's letter requests Information to conduct an investigation and oversight. 
However, Waxman's position is not consistent with the Speaker's position on an impeachment investigation. The Speaker contradicts Waxman, and says that no investigation is possible; and that regardless the results of that investigation, no impeachment is allowed. 
By implication, Pelosi's decision -- without an investigation, to remove impeachment as an option -- falls short of her legal duty.
When we have facts after that impeachment investigation, we will know whether the right decision is to do nothing, file charges, or discuss another option.

The Constitution only delegates to the House, not the Speaker, the power to impeach; or not impeach. The House must explain why "oversight" excludes conducting an impeachment investigation.

The House Ethics Committee must understand:

A. Why is the Speaker removing legal options without conducting an investigation;

The Speaker is not doing her duty, as required by oath.

B. What evidence -- without an investigation -- does the Speaker have behind her "decision" to remove impeachment as an option;

The Speaker has no evidence.

C. What evidence does the Speaker have behind her contention that an investigation will be a threat to the Constitution;

The Speaker has no evidence.

D. How does Speaker Pelosi reconcile her position -- that an investigation is not possible or permitted for partisan agendas -- with Waxman's assertion -- that an investigation is required to conduct oversight;

The Speaker cannot reconcile her position on impeachment with Waxman's letter.

E. What evidence does Speaker Pelosi have proving that an investigation into the President will be a threat to the Constitution;

The Speaker has no evidence.

F. What evidence does Speaker Pelosi have proving that blocking an investigation is permitting under her duties as Speaker; or brings credit upon the House;

The Speaker has no evidence.

G. Who was the source of the information, argument, or data which the Speaker used to assert that an impeachment investigation or an impeachment would be a threat to the Constitution, a threat to the DNC agenda, or a threat to the Nation's security.

The Speaker has not disclosed who provided her with what data to justify her assertion. This smacks of the same baseless assertion the President made about Iraq WMD and an imminent threat: Illusory.