Supreme Court nominee Brett M. Kavanaugh faces the Senate Judiciary Committee on Capitol Hill on Sept. 5. (Saul Loeb/AFP)

Brett M. Kavanaugh is a liar. He has fudged the truth (either provably or almost certainly) on everything ranging from slang in his high school yearbook to documents stolen from Senate Democrats during the George W. Bush years. We can come up with all sorts of theories about why Kavanaugh does this. But his personality is secondary to a bigger issue: Kavanaugh’s tall tales are part of a larger ecosystem. The Republican Party, as part of its quest for power, has been waging a battle with the truth for decades.

Kavanaugh may believe that the allegations of sexual misbehavior as well as other misconduct now leveled against him are a vendetta created by Democrats. But it is Republicans who have created an echo chamber for falsehood for political gain and who have been routinely doing so for almost 40 years. It was Ronald Reagan who once claimed trees cause more pollution than cars, as a way of playing down the environmental damage caused by the latter. It was also claimed that tax cuts in the early 1980s would pay for themselves. Instead, the deficit soared. (Treasury Secretary Steven Mnuchin made a similar claim last year about President Trump’s tax cuts. It was equally inaccurate.)

Kavanaugh’s role in the Republican ecosystem of lies goes back to the Clinton administration. As part of independent counsel Kenneth W. Starr’s investigation into the Whitewater land deal — which turned out to be giant nothingburger — Kavanaugh spent nearly three years attempting to prove a right-wing conspiracy theory that Clinton White House staffer Vincent Foster did not die by suicide. Kavanaugh did this despite the fact he personally believed those theories about Foster’s death were bogus. This is cynicism taken to an almost mind-boggling degree.

Over time, as treating lies like this seriously became routine, the GOP went from a willingness to tolerate politicians (not to mention talk radio hosts) saying anything, as long as they closed the sale, to seemingly failing to distinguish between the con and the truth. When Barack Obama was elected president, Republicans quickly set about creating an alternative reality in which his election was a fiction — remember ACORN? — and his major initiatives would bring about the apocalypse. The Affordable Care Act’s origins were rooted in conservative circles, but Republicans — beginning with Sarah Palin — claimed the bill would set up “death panels” where anonymous bureaucrats would decide in individual cases who would receive treatment and who would be let to die. There were claims that the housing and financial crisis was mainly caused by government programs and mandates that forced unsuspecting banks to lend money to people who couldn’t keep up with their bills. Global warming was increasingly dismissed as a hoax.  By the time Mitt Romney ran for president in 2012, he lied so frequently about Obama’s record, the New York Times took him to task, claiming, “Mr. Romney’s campaign rests on a foundation of short, utterly false sound bites.” And there was the spread of birtherism: The myth that Obama entered the world in Kenya took on such a life in the GOP that by 2016, only 27 percent of Republicans believed Obama was definitely born in the United States.

One of those birthers? Donald Trump. Trump, of course, is in a league of his own when it comes to lies – last month, The Post’s Fact Checker team estimated he’d made more than 5,000 “false or misleading claims” since becoming president. Here’s a typical example: This past weekend, at a rally in West Virginia, Trump claimed he would always protect Americans with preexisting health conditions. In fact, the Trump Justice Department is refusing to defend that part of the Affordable Care Act in court.

Republicans have not considered Trump’s trouble with the truth, apparent to anyone even before the campaign, to be disqualifying. His successful campaign depended on a cavalcade of falsehoods, ranging from a crazed obsession with Hillary Clinton’s emails, to fake news pushed on Facebook and Twitter feeds in a Russian-sponsored misinformation campaign. Nor are Republicans now, as a group, embarrassed by his lying, though they should be. Last year, a poll conducted by Firehouse Strategies found a majority of Republicans surveyed believe Trump “exaggerates only with good intent.”

But that’s not how lying works, not over the long run. Lying becomes circular. Repeat a lie often enough, and people will believe it. The ongoing existence of the lie itself changes the debate. Then it leads to even more acceptance of lies and lying. Shortly after Trump was elected, David Muir at ABC asked him if it was a problem to talk about voter fraud without producing any evidence. The president’s response? “No, not at all, because many people feel the same way that I do.

None of this is to say the Democrats or those on the left are fully honest. But only one party has anointed a world-class liar as its standard-bearer. Only one considers routine lies an acceptable way of doing business. Kavanaugh’s tour de force of truth shading and anger in front the Senate Judiciary Committee last week was just another entry on this sorry ledger.

Read more:

Paul Waldman: All of Brett Kavanaugh’s lies, distortions and absurdities

Chris Coons: Here’s what the FBI investigation into the Kavanaugh allegations should look like

Jennifer Rubin: So many lies, so little time to investigate

Greg Sargent: Republicans have a strategy to save Kavanaugh. It exposes Trumpism at its worst.

Andrew Manuel Crespo: Brett Kavanaugh, take a polygraph