I have written this piece for Slate. Here is my key point:

What Democrats need, then, is a clean impeachment strategy laser-focused on the Ukraine allegations. The allegation is easy to understand and does not require a Carrie Mathison cork board connecting the cast of characters with yarn. President Trump solicited a foreign government to provide dirt, perhaps manufactured, on one of his political rivals, Joe Biden, who he may face in the 2020 presidential election. Trump did so while the United States was withholding crucial financial aid from the Ukraine, reportedly at his behest alone. Trump professed a concern about “corruption,” but so far as we know the only supposed corruption he has ever expressed any concern about involved generally unsubstantiated allegations about Biden’s family, or other personal political and legal foes.

The story is clear whether we hear from the whistleblower directly or not. The President has admitted the conduct; he disputes only its wrongfulness, describing his call as “very legal and very good.” And already today there is enough for the House to conclude that the president has abused his power and is worthy of impeachment. That’s true whether or not the solicitation of foreign opposition research is a campaign finance crime—I believe it is and Special Counsel Robert Mueller suggested it could be illegal as well even as he raised what he considered to be First Amendment issues—and it is true whether or not Trump’s conduct as reported in the partial summary of the conversation with Ukraine’s president amounted to the crime of extortion or bribery. The mafia-like shakedown by Trump—along the lines of: That’s a really nice country you have; it would be a shame if something happened to it—needs to be condemned whether it amounted to a technical violation of the law or not.

And this is the key point: the ordinary argument that an impeachment close to the election is unnecessary because the voters can decide whether or not to keep the president in office does not hold water when the impeachable conduct involves attempting to manipulate the election process itself. It is indeed a matter of national security if the president is seeking to use the power of his office—and potentially hundreds of millions of dollars in taxpayer money—to get a weaker foreign government to do his bidding in coordination with his personal lawyer.
Sure, the Republican-dominated Senate might not convict the president with a necessary two-thirds vote if the House impeaches (although the silence from many Republican Senators suggests they are still deciding what do to). But impeaching the president for an abuse of power in soliciting foreign help in the election will serve three purposes even if there is no conviction and removal from office.