WASHINGTON — At the heart of the impeachment case against President Donald Trump lies a potential dagger for his re-election campaign: He's accused of putting himself first — and American interests second.

So the president's problem isn't just that the Ukraine affair has potentially provided the House with the substance of an impeachable offense. It's the fact that the very same alleged activity — abusing his office to help himself — cuts against his core political message of always placing "America first."

"The more we read about this story, it highlights what we’ve come to know over the last couple of years, which is he might be in the Hall of Fame of self-interest," said Rory Cooper, a former House GOP leadership aide and managing director of the communications firm Purple Strategies who argued Tuesday that Republicans must publicly describe the president's conduct as wrong.

Cooper recalled Trump running in 2016 on "the idea that he was going to fight for people that no one else was fighting for" while he portrayed his opponent, Hillary Clinton, as corrupt and self-dealing.

"The only 'victim' that Donald Trump is fighting for anymore is himself," Cooper said.

Incredibly, it was Trump's White House that voluntarily released the summary of a phone call transcript containing what his critics point to as plain evidence of misplaced interests — a release that was reportedly at odds with the instincts of more seasoned political players like Vice President Mike Pence.

Perhaps Pence understood that evidence that Trump was using the power of the presidency to try to secure his own re-election — or even just boosting the perception that he tried to do so — could be devastating in the midst of an impeachment push by House Democrats and as the two men campaign for a second term.

Since 2014, Congress has provided about $1 billion in aid to Ukraine to counter Russian aggression — a policy deemed to be in the national security interests of the U.S. by lawmakers and both the Obama and Trump administrations. But for several months this year, the Trump administration withheld a planned $391 million injection of support to Ukraine without explanation. Then, in September, after a phone call between Trump and Ukrainian President Volodymyr Zelenskiy, Trump released the money.

When the money was headed to Ukraine, that was in America's stated interest.

In holding it back, Trump was subordinating that interest to something else — but not explaining his motives publicly or to Congress.

"I have no idea what precipitated the delay," Senate Majority Leader Mitch McConnell, R-Ky., who was a major advocate for providing the money, told reporters late last month.

The summary of Trump's remarks in the phone call provided a possible answer.

"I wouldn't say that it's reciprocal necessarily because things are happening that are not good, but the United States has been very, very good to Ukraine," Trump said early in the call.

Zelenskiy replied by praising Trump for the U.S. effort to assist Ukraine and noted that "we are almost ready to buy more Javelins from the United States for defense purposes," referring to a type of missile.

Trump then asked Zelenskiy for two things: facilitation of efforts by Attorney General William Barr and Trump's personal lawyer, Rudy Giuliani, to investigate the company Crowdstrike, and an investigation into former Vice President Joe Biden — Trump's top rival for the presidency in 2020, according to polls — and his son Hunter Biden.

After the phone call with Zelenskiy, in which he was assured that the new prosecutor would play ball, Trump released the $391 million. That decision realigned U.S. policy with stated U.S. interests in the region. The question Democrats are asking now — and in some cases phrasing directly as an accusation — is whether the order of operations shows that Trump used his authority to put his own interests ahead of his country's.

Full coverage: Trump impeachment inquiry

In issuing a subpoena to Giuliani this week, House Foreign Affairs Chairman Eliot Engel, D-N.Y., wrote that there were "credible allegations" Trump's lawyer "acted as an agent of the president in a scheme to advance his personal political interests by abusing the power of the office of the president."

Alexander Hamilton explained impeachable offenses as involving "the abuse or violation of some public trust."

It's possible that simply withholding the money would constitute an abuse of power. Conversely, there might be some question as to how some may view Trump's decision to suspend the funds — turning from a policy that aligned with America's support of Ukraine to one that didn't and back to one that did over a short period of time — rather than block them permanently.

But the allegations of self-dealing against Trump — both with regard to Ukraine and other matters — are serious enough that a shades-of-gray discussion may be too academic for the moment, said Kim Wehle, author of "How to Read the Constitution and Why" and a law professor at the University of Baltimore.

"We can talk about a sliding scale at a different time," she said. "This is off the deep end."

Trump is fighting back with full force.

He has said repeatedly that the chairman of the House Intelligence Committee, Adam Schiff, D-Calif., should be criminally charged for caricaturing the contents of his call with Zelenskiy at a hearing last week, and he has termed the whistleblower's whose complaint brought the Ukraine affair to light as a spy who should be outed.

Why isn’t Congressman Adam Schiff being brought up on charges for fraudulently making up a statement and reading it to Congress as if this statement, which was very dishonest and bad for me, was directly made by the President of the United States? This should never be allowed! — Donald J. Trump (@realDonaldTrump) October 1, 2019

He and his allies note that Hunter Biden had no particular qualifications for the $600,000-a-year seat he occupied on the board of a Ukrainian gas company. And they contend, against the available evidence, that Joe Biden acted corruptly by threatening to withhold aid to Ukraine if the country didn't fire a particular prosecutor who had investigated that company (the probe had ended before Hunter Biden was hired for the board and Joe Biden's threat was consistent with U.S. policy and rooted in the prosecutor's lack of action to root out corruption, not his aggressiveness against it).

Of course, none of that addresses the central question of whether Trump's efforts to discredit the investigation into his 2016 election — involving the Crowdstrike conspiracy theory he is pursuing — and dig up dirt on the potential 2020 opponent about whom he is most concerned constitute the abuse of his office.

If the House determines through an impeachment vote that he violated the public trust by putting his own interest before American national interest — particularly if even a small number of Republicans agree — Democrats will have new ammunition to try to poke a hole in the umbrella "America First" message he uses to define his priorities.

One Trump ally who worked on his 2016 campaign said the partisan divide may be too strong for that.

"Democrats made that same argument in 2016 and it didn't work then, and I'm just not sure how effective it really will be now," the former aide said. "The people who believe it will believe it, the people who don't believe it already won't believe it, and I don't think that's an argument that will move people in the middle."

But the existential risk for Trump — beyond impeachment — is that it might.