The battle for American hearts and minds in the unfolding impeachment drama is, at its core, a battle between two very different California congressmen.

In the red corner is Devin Nunes, a Republican former dairy farmer from the state’s agricultural Central Valley, who long ago threw his lot in with Fox News talking-point orthodoxy and has never hesitated to defend Donald Trump, no matter how much the rest of the political establishment – and the factual record – was arrayed against him.

In the blue corner is Adam Schiff, Democrat of Los Angeles, who in January took over Nunes’s gavel as chair of the House intelligence committee, and has dug deep into his experience as a federal prosecutor to distill the complexities of a political intrigue spanning halfway around the globe into an easily digestible indictment of the president.

As the two senior lawmakers on the intelligence committee, the pair has emerged as Trump’s chief defender and chief nemesis, highly visible surrogates but also lightning rods of the broader political struggle. Both have earned lopsided quantities of praise from their own partisans and boundless scorn from the other side of the aisle.

Their styles could not have contrasted more sharply than when they made their opening statements in the public impeachment hearings on Wednesday. Schiff was cool, forensic, quoting witness statements and established facts, outlining what he saw as the key questions before Congress and the American people.

The outcome of the impeachment process, Schiff said, would affect “not only the future of this presidency but the future of the presidency itself, and what kind of conduct or misconduct the American people may come to expect from their commander-in-chief”.

Nunes was indignant and blustery, sweat pricking at his brow as he reeled off a litany of supposed plots, conspiracies and low conniving by everyone except the person the members were there to investigate – the president of the United States.

The Democrats, he charged, were “the last people on Earth with the credibility to hurl more preposterous accusations at their political opponents”. They were waging a “scorched-earth war” in a “cult-like atmosphere” and putting witnesses through “Star Chamber” interrogations before deciding if they were fit for prime-time exposure.

On the key question of whether Trump had pressured Ukraine into providing political dirt for his re-election campaign, however, Nunes remained largely silent.

In some ways, Schiff and Nunes are acting as one would expect lawyers to act in a courtroom, seizing the best arguments at their disposal and running with them. Schiff has close to a cast-iron case that Trump did indeed demand political favors from Ukraine in exchange for US military aid and other vital forms of assistance; the only real question is whether they amount to the “high crimes and misdemeanors” required by the constitution to justify removing a president mid-term.

Without such an advantage, Nunes is instead seeking to undermine the credibility of the people making the case against Trump, to question the reasons why the impeachment process began at all, and to muddy up the factual record with dark hints of Democratic party plots, collusion with key witnesses and outright deception.

But beyond this tussle for the rhetorical upper hand lies a deeper and more consequential issue: whether Congress is capable of exercising its constitutional independence as a check on executive power, as it ultimately did during the Watergate scandal, or whether partisanship in 2019 has devolved to a point where party interest reigns supreme and nothing else – not even the sale of America’s foreign policy for political favors – really matters.

Long before Trump entered the political scene, Nunes had a reputation as someone willing to toe the party line without question. As chair of the intelligence committee from 2015-2019, he was part of a years-long (and ultimately unsuccessful) quest for evidence of wrongdoing by Hillary Clinton in the lead-up to the deadly 2012 attack on a US diplomatic compound in Benghazi, Libya.

After Trump came into office, Nunes made it his job to protect Trump at all costs against allegations that his campaign had welcomed or even colluded with Russian interference in the 2016 presidential election. Nunes rejected the unanimous conclusions of the intelligence services – over whom he was charged with exercising oversight – that Russia had indeed interfered. And he made a notorious cloak-and-dagger trip to the White House to accuse those same intelligence services of mounting a deep-state espionage operation against Trump and his allies. (The charges he made did not stick.)

Not only did Nunes clear Trump of any collusion with Russia; he turned right around and started investigating the FBI’s reasons for opening the investigation in the first place, thus feeding straight into the sort of deep-state conspiracies beloved of Fox News hosts and Trump’s inner circle. Other Republicans, fearful of the Trump-supporting party base, followed him some of the way along this path but he was one of the very few to go so far, and so publicly.

Senior Democrats – not Schiff – began referring to Nunes as “Trump’s stooge” and “Trump’s fixer”. And when Schiff pushed back, he came in for his own typically Trumpian form of abuse. One tweet, memorably, called him “little Adam Schitt”.

Schiff has played a principal role in the House’s investigation into the Trump campaign and Russia’s interference in the 2016 election, the subject of Robert Mueller’s investigation. He’s been more reluctant than some of his more gung-ho fellow Democrats to call for the impeachment of the president and came around only when Nancy Pelosi, the equally reluctant speaker, concluded that the Ukraine affair was too grave to overlook. What the New York Times has described as Schiff’s “more-in-sorrow-than-in-anger tone” has been a big part of his appeal across all parts of his party.

The darkest interpretation of the standoff is that Nunes is part of an attempt by Trump and his supporters to destroy the very notion of investigative fact and replace it with a series of partisan talking points – that the investigation is a “sham”, that Schiff should himself be investigated, that Trump’s call in which he openly asked the Ukrainian president to “do us a favor” by investigating Hunter Biden was “perfect”, and so on.

Another way of looking at it, though, is through opinion polls that suggest the case for impeachment is growing stronger, not weaker, with the American public. The CNN political analyst Brian Stelter put it this way on Wednesday: “Schiff is trying to speak to the entire country. Nunes is only speaking to the Trump base and the Fox audience.”

It’s pretty clear, meanwhile, which man is doing better in his own home district. In last year’s midterms, Nunes saw his previous 35 percentage-point advantage over his Democratic challenger shrink to just six points, turning a rock-solid Republican seat into a swing district. Schiff, by contrast, was returned with close to 80% of the vote.