The US House of Representatives possesses the sole power of impeachment of US officials.
"The House brings impeachment charges against federal officials as part of its oversight and investigatory responsibilities. Individual Members of the House can introduce impeachment resolutions like ordinary bills, or the House could initiate proceedings by passing a resolution authorizing an inquiry. The House Committee on the Judiciary ordinarily has jurisdiction over impeachments, but special committees investigated charges before the Judiciary Committee was created in 1813. The committee then chooses whether to pursue articles of impeachment against the accused official and report them to the full House."
But does the House have a duty to impeach when it is clear that impeachable offenses have occurred, or is it discretionary? If it is discretionary, does that mean that the decision can be based on unspecified grounds, or must the grounds be explicitly stated? If a reason is required, would a statement such as, "We think it would be inadvisable to impeach Mr. X at this time." be acceptable?
I ask because the House is not providing an explicit reason why they are undecided on this issue in the face of Trump's multiple obvious impeachable offenses.