Last week, as the public phase of the impeachment inquiry started, I wrote in this space that it was important for Americans to pay attention to the hearings. It turns out they were more important, more illuminating than I imagined they would be. This week promises to be even more impactful.

After last week’s testimonies and revelations, Republicans are in a quagmire as to just how to defend the indefensible actions of a president who sought to withhold congressionally mandated military aid to Ukraine unless that country’s government initiated an investigation into Trump’s main political rival, former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE, and his son, Hunter Biden.

Their main talking point before last week was that everything the witnesses described was “hearsay.” They complained that none of the witnesses thus far had listened in on President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE’s phone call to Ukraine’s president and that those witnesses didn’t have firsthand knowledge from the president about the issues surrounding aid to Ukraine.

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That point went up in smoke after the testimony of David Holmes, the aide to acting ambassador to Ukraine, Bill Taylor. Ambassador Taylor had mentioned his aide in his public testimony last week as having heard firsthand of Trump’s intentions. Holmes, according to Taylor, had overheard a conversation between Gordon Sondland Gordon SondlandGOP chairman vows to protect whistleblowers following Vindman retirement over 'bullying' Top Democrat slams Trump's new EU envoy: Not 'a political donor's part-time job' Trump names new EU envoy, filling post left vacant by impeachment witness Sondland MORE, Trump’s ambassador to the European Union, and Trump.

Afterwards, Sondland described Trump as “not giving a shit about Ukraine, only about the big stuff” — meaning the investigation of the Bidens that Ukraine was supposed to undertake in exchange for $400 million in military aid Congress had already approved.

While the majority of Holmes’ testimony was behind closed doors, his opening statement was made public, and it’s worth paying attention to.

The other bombshell testimony last week was from former Ambassador to the Ukraine Marie Yovanovitch Marie YovanovitchGrand jury adds additional counts against Giuliani associates Lev Parnas and and Igor Fruman Strzok: Trump behaving like an authoritarian Powell backs Biden at convention as Democrats rip Trump on security MORE, who was recalled and let go from her duties after a concerted smear campaign apparently led by Trump’s private lawyer gone rogue, Rudolph Giuliani, as he pranced around Ukraine badmouthing her.

Ambassador Yovanovitch was the epitome of composure, professionalism, non-partisanship, patriotism and dedicated public service. And what did Trump do in the middle of her somber testimony? He tweeted misogynistic attacks against her that were very clearly designed to intimidate her and to undercut her testimony. The illegality of Trump’s witness-tampering (in real time) aside, what he did was despicable; it suggested he was terrified of what the ambassador had to say.

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The public testimony of another diplomat, George Kent, the deputy assistant secretary of state for European and Eurasian Affairs, combined with Taylor’s and Yovanovitch’s, underscored the value of these diplomats’ accounts in helping Americans to understand just how Trump tried to manipulate the issue of military aid to Ukraine in order to extort an investigation of the Bidens.

Sometimes infused with drama — but always straightforward and apolitical — the testimonies of these three dedicated public servants helped paint a picture of how the Giuliani maneuverings around U.S. foreign policy in Ukraine helped to muddy the waters and swing the pendulum of priorities towards Trump’s private political obsessions, instead of the interests of the country he was elected to lead.

Voters need to understand that Trump is not interested in furthering U.S. foreign policy — only in furthering his own political interests.

Contrary to another ridiculous Trump and GOP talking point, the president has no interest in rooting out corruption. If he did, he would have discussed corruption with the president of Ukraine. His only interest was to gain political advantage over Joe Biden, the person he sees as his most dangerous political rival in 2020.

Viewers are hearing and seeing testimony this week from Jennifer Williams, an aide to Vice President Mike Pence Michael (Mike) Richard PenceFormer Pence aide: White House staffers discussed Trump refusing to leave office Pence vows for law and order everywhere Trump met with chants of protest as he pays respects to Ruth Bader Ginsburg MORE, who has testified privately that she heard the phone call between Trump and Zelensky. She said that “Trump's request for investigations into the Bidens struck her as “unusual and inappropriate” and that it “shed some light on possible other motivations” Trump had to halt aid to Ukraine.

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Her testimony has already been ripped by Trump, who is clearly upset that she is daring to testify; it shows yet again how afraid Trump is of the truth. They will hear from a much-anticipated witness, Amb. Sondland, who could be in some legal jeopardy if he does not come clean to Congress about what he discussed with Trump on the call David Holmes overheard.

If Sondland testifies truthfully, it will be perhaps the most damning testimony to date for Trump, and one that may prove that Trump specifically asked Zelensky for an investigation of Biden before the U.S. would approve the disbursement of the $400 million in military aid that Ukraine so desperately needed.

Per House Speaker Nancy Pelosi Nancy PelosiDemocratic senator to party: 'A little message discipline wouldn't kill us' Overnight Health Care: New wave of COVID-19 cases builds in US | Florida to lift all coronavirus restrictions on restaurants, bars | Trump stirs questions with 0 drug coupon plan Overnight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds MORE (D-Calif.), if this is proven through firsthand testimony, it could describe Trump’s attempt to bribe a foreign power — a clearly impeachable offense, according to the Constitution.

The truth is powerful, and no amount of gaslighting or spin from a frightened Donald Trump can hide the reality that the president tried to abuse his powers. Americans should stay tuned in. If they do, they will understand the importance of taking that power away from him in 2020.

Maria Cardona is a principal at the Dewey Square Group, a Democratic strategist and a CNN/CNN Español political commentator. Follow her on Twitter @MariaTCardona.