(Bloomberg Opinion) -- Today, the Senate is expected to vote against removing Donald Trump from office. But what will be the verdict of history?

In the glass half-empty scenario, Trump’s claims to have been completely exonerated will be embraced by future Americans and their presidents. High crimes and misdemeanors will be defined down to a bare minimum, and maybe out of existence altogether. The impeachment provisions of the Constitution will become more or less a dead letter — except, perhaps, in the extremely unusual circumstance where a president’s party holds less than a third of the seats in the Senate. Future presidents will embrace dirty tricks to win re-election, safe in the knowledge that the Trump precedent makes their removal vanishingly unlikely. The Democratic House’s party-line impeachment will be seen as a partisan act, not a genuine manifestation of constitutional outrage.

There is, however, a glass half-full scenario as well. History may come to judge Trump’s conduct, highlighted by his impeachment and underscored by the historical record, as a blatant violation of constitutional norms. That in turn could lead future presidents to avoid Trump-like conduct to avoid the shame and embarrassment of impeachment. The correct constitutional meaning of high crimes and misdemeanors would be indeterminate; but the fact that the majority of the House deemed Trump’s conduct impeachable would provide sufficient reason for future presidents to steer clear. In this future, the Republican Senate’s vote to acquit will come to seem partisan and craven, and the House vote will look truth-seeking and brave.

Which scenario will come to pass depends very much on whether Trump wins re-election in November. Unlike Richard Nixon and Bill Clinton, Trump’s misconduct came in his first term, not his second. As a result, in Trump’s case, his re-election or defeat will inevitably have a large effect on the meaning of his impeachment.

If Trump wins, it will be easy for his defenders to say that the impeachment contradicted the will of the American people. A re-election could then be characterized as a public repudiation of the impeachment charges and a vindication of the president. This is especially true if Trump’s victory is significant — say, a meaningful popular-vote majority for Trump with coattails that help Republicans hold the Senate.  

However, if Trump is defeated, especially by a significant popular majority, Democrats will be able to claim that the people voted in accordance with the House majority that voted to impeach. If the Senate were to flip to a Democratic majority, Democrats can further argue that the public rejected the Senate’s vote not to remove Trump — a party-line (or near enough) vote by senators who represent well under half of the national population despite being a majority in the Senate. From these conclusions it would follow that, in important ways, the constitutional system succeeded despite being temporarily thwarted by Senate Republicans: Trump committed wrongdoing; he was impeached; and he paid the political price of removal.

What’s unfortunate about all of this is that in November, the public won’t be voting directly on whether Trump committed high crimes and misdemeanors. Instead, like all presidential elections, the 2020 vote will pose a binary choice between Trump and a Democratic candidate. (Unless there’s a third-party candidate, which could be a disaster of a different kind.)

Binary elections demand that the voter choose the least bad option. There could be Republicans in the United States who genuinely believe Trump committed high crimes and misdemeanors and should be removed from office, but still prefer Trump to his Democratic challenger. Conversely, there might be Democratic voters who think Trump should be removed, but stay home on Election Day.

Regardless, the outcome of the presidential election will hinge on many issues — social, economic, and foreign policy-related — that aren’t officially on the table in the impeachment proceedings. Interpreting impeachment in the light of the election will be a kind of historical fiction, or at least the kind of retrospective interpretation that belongs more to morality and politics than to pure historical or legal analysis. No matter the outcome, the election will be something more than a replay of the impeachment fight.

This leads to a concluding question: Is there any possibility that, even if Trump is re-elected, the impeachment would still have some constraining effect on future presidents, rather than an enabling one? If so, the impeachment effort would not have been in vain.

The answer is a qualified yes. Not every president will enjoy Trump’s apparently immovable popularity with his base. That means future presidents will have to fear impeachments that dislodge their support by revealing disturbing facts about how they have done their jobs. Knowing that impeachment is a possibility — even impeachment without removal — could still function as a limited form of deterrence on future misconduct.

That possible deterrence is admittedly a slender reed on which to rely in imagining the conduct of future presidents. But if the glass half-empty scenario is fully realized, American constitutional democracy is in serious trouble.

The erosion of democratic norms takes years and even generations. It would be a mistake to expect the collapse of the Republic overnight. Yet gradual erosion is erosion still. If someday — may it never happen! — the story of the constitutional erosion of U.S. democracy needs to be told, the vindication of Trump and his conduct will surely be an important chapter.

To contact the author of this story: Noah Feldman at nfeldman7@bloomberg.net

To contact the editor responsible for this story: Sarah Green Carmichael at sgreencarmic@bloomberg.net

This column does not necessarily reflect the opinion of Bloomberg LP and its owners.

Noah Feldman is a Bloomberg Opinion columnist. He is a professor of law at Harvard University and was a clerk to U.S. Supreme Court Justice David Souter. His books include “The Three Lives of James Madison: Genius, Partisan, President.”

©2020 Bloomberg L.P.