There is political wisdom in not attempting to throw the kitchen sink at Trump. Impeachment should focus on Trump's misdeeds while in office. Hush money payments made prior to his election should not be a focus. "Collusion" with Russia during the 2016 presidential campaign should not be a focus. Long term financial ties with Russia that may lie hidden in Trump's tax returns should not be a focus. There may be ways those can be referenced to provide context during hearings, but they should not constitute separate counts
In that sense the impeachment investigation should be narrowly focused, on actions that have happened since Trump took his oath of office. But it is unwise to narrow the impeachment inquiry down to a single "High crime or Misdemeanor." Trump needs to be removed for far more than just his role in the "Ukraine Conspiracy", grave as that may be. But, more to the point, he needs to be accused by the House of more than that alone.
By all means let the Ukraine charge take the lead. It is distinct and straight forward to prosecute. Unlike the wide scale undermining of the United States Constitution, it involves violating America's national security in an easy to grasp and tangible way. Trump's conduct toward the Ukraine may well be the easiest article of impeachment to convict him of, but it should not be the only one prosecuted. It needs to be pressed within a broader context that additional charges would provide.
Ultimately only a single article of an impeachment indictment against the President needs to pass the House in order for impeachment to move forward, but that does not argue in favor of presenting a single charge only. Some Democrats worry about muddying the waters with too wide a scope of inquiry. I worry about the opposite. A pattern of wide scale Presidential misconduct in office must be presented, otherwise Trump and his allies can focus their disinformation campaign on the particulars of one confined set of facts.
As has been shown before, truth is no deterrent to a Trumpian line of defense, which never revolves around the winning of any argument. Instead their goal has always been to confuse the public with alternate versions of reality that literally turn facts on their head. That is how and why the waters get muddied, to Trump's advantage, and Democrats must not fall into it. Already Trump’s enablers are deflecting attention away from the crime and onto the so called “accusers.” This is what they always do. The "guilt or innocence" of Donald Trump can not rest on the facts of any single act alone, no matter how consequential it may be. When presented with a discreet accusation, Trump is a master at expanding the "shadow of a doubt" into a dust storm induced blackout, blinding the public of the ability to discern fake from real news with any degree of certainty.
Trump's actual impeachment likely will ultimately rest on Congressional findings regarding the Ukraine, but that by itself could mean winning the battle while losing the war if, in the process, Democrats do not forcefully inject into the record substantial evidence establishing that Presidential misdeeds relative to the Ukraine are consistent with the entire tenor of Trump's Administration and his time in office. That is why additional counts in the final articles of impeachment presented against Donald Trump become critical. It is not just Trump's actions in any instance that must be prosecuted, it is the fundamental integrity of the man who occupies the Oval Office that must be frontally assaulted relative to all of his actions and every misinformation campaign subsequently he launches in his defense. One count of impeachment does not sufficiently present a pervasive pattern of Trump's core unfitness to hold office. It should and must be buttressed by other charges, based on his actions while in office centered on the Obstruction of Justice and his self serving corruption at the expense of the American people.
Additional impeachment counts need not comprehensively catalog every possible instance of presidential abuse. Congress has a bottomless supply of obstruction charges to choose from, and as for self serving fiscal corruption, there too there is much to pick between: Trump ‘“suggesting” that VP Pence stay at a Trump property on the opposite side of Ireland while Pence was there on State business. Trump “proposing” that a G7 Summit would best be hosted at his own resort in Florida. Air Force crews getting routed to stay over at a Trump resort in Scotland. Perhaps petty in the big picture, but useful in emphasizing how petty is the man who now occupies the oval office. It is Donald Trump in his totality who must be fully discredited, and that requires multiple counts of impeachment against him.