Quid pro quo is the phrase of the month in US politics and it could be the key to the impeachment of President Donald Trump. The Latin phrase means “something for something” and that is what Trump has been accused of trying to arrange with the new president of Ukraine, Volodymyr Zelensky.

That something for something — that quid pro quo — has been characterized as unconstitutional and even criminal and thus sufficient ground for impeachment. Of course Trump has vehemently and repeatedly denied it, even while White House insiders who have direct knowledge of the circumstances have admitted it in depositions before the US Congress.

A quid pro quo is not, by itself, illegal or immoral. It depends on what that “something” is which is being exchanged for “something.”

For instance, in the movie business the “something” a director may offer could be a lead role in exchange for sexual favors. That is immoral. In politics, the “something” offered is usually a lot of money in exchange for a government contract. That is illegal.

In foreign affairs or in the relationship between countries, it could be a trade or defense quid pro quo. The parties may be of unequal economic or military capability, in which case the stronger country may tend to make the weaker one an offer it cannot refuse (sometimes referred to as a Godfather offer).

America has often had such a relationship with other countries, the Philippines among them. While such a quid pro quo may leave a bad taste in the mouth, it is neither immoral nor illegal but just one of the harsh facts of life.

An economic quid pro quo is something that Trump is not famous for — in fact he is notorious for getting something without paying for it, as several suppliers have testified (as one Republican congressman put it, “More quid and no quo!”). On the other hand, Trump has been accused of what could be described as a moral quid pro quo, having been exposed of paying off a porn actress and a Playboy bunny to keep quiet about their illicit affairs with him.

Trump’s current problem arose from a foreign affairs situation — America’s relations with Ukraine. It could have been one of those instances where a stronger country pressured a weaker country on such issues as trade or ideology — and while that could have left a figurative bad taste in the mouth of the weaker party, that would not have been illegal, much less unconstitutional.

When the US won the Spanish-American war, Spain had to give up claims of sovereignty over Cuba, Puerto Rico, and Guam and had to give up the Philippines for $20 million in the Treaty of Paris.

After the British Empire defeated the Qing dynasty in the first Opium War, China had to cede Hong Kong to the British. And after China lost the second Opium War, the British forced the Qing dynasty to cede Kowloon and lease the new territories for 99 years.

Those were examples of a quid pro quo where the “something” that the victors gave the losers was peace in exchange of territories. A very lopsided quid pro quo but “somethiing for something,” nonetheless.

When the US gave the Philippines back its independence, one of the conditions was what Don Corleone would have imposed. The Philippines had to agree to give the US equal rights to exploit the country’s natural resources. That condition had to be grudgingly accepted.

Another condition was the continued presence of US military bases in the Philippines. In an international environment where imperialist countries were like sharks waiting for prey, looking for weak nations to usurp, that was a condition necessary for the survival of the newly independent nation.

This kind of quid pro quo was what acting White House Chief of Staff, Mick Mulvaney, probably meant when he admitted that the US “does it all the time” in its dealings with other countries.

Unfortunately for Mulvaney, he had responded to a question from the media specifically about Trump’s phone call to the Ukranian president. The “something” Trump wanted was dirt on a potential rival in the 2020 presidential elections, allegations of corruption involving former Vice-President Joe Biden and his son, Hunter Biden.

Also “requested” by Trump was a probe into alleged Ukranian, rather than Russian, meddling in the 2016 elections — a wild theory debunked by US intelligence agencies.

What’s more, the “something” that Trump was withholding was over $400 million in aid already appropriated by the US Congress and which Ukraine desperately needed.

White House insiders have confirmed in testimony before Congressional committees that Trump had made the release of the funds contingent on the public announcement by the Ukranian president that his government would initiate the investigations Trump wanted.

The quid pro quo required by Trump, according to the Democrats, the media, and even by some Republicans in effect invited a foreign country to get involved in the US electoral process — a conclusion that the report of Special Counsel Robert Mueller could not make about Trump in the case of Russia’s meddling in the 2016 elections.

The Democrats believe they have the goods on Trump and can move to impeach him. Of course, the battle will still have to be fought in the Republican-controlled Senate.

The question is will the Republicans’ loyalty to their country end where their loyalty to Trump and the party or their political interests begin?

Who knows? President Richard Nixon was a Republican like Trump. But he was pressured to resign by fellow Republicans who were more loyal to their country than to their personal interests.