The United Kingdom's Home Office has a national security webpage delineating the warning signs of "radicalization," and it provides a remarkably accurate description of the political left here in America. 

(1) Becoming increasingly argumentative

When was the last time Democrats looked happy about anything?  For them, we are in a perpetual state of danger and misery.  Unconscious racism taints everything in America.  Masculinity is toxic.  Carbon dioxide emissions — the very gas we exhale with each breath — guarantee the planet's doom in five or ten or twenty years' time.  Math is racist.  Merit is racist.  Working hard, owning a home, getting married, and having children are all threateningly normative.  Virtue and vice are too judgmental.  The representative image of the Democratic Party is no longer FDR or JFK; it is the indelible video clip of a young woman screaming at the sky on the day of President Trump's inauguration.  

(2) Refusing to listen to differing points of view or engage with others who are different

"The science is settled," the left argues, so there is no reason to use the scientific method or cost-benefit analysis to determine whether tens of trillions of dollars in global spending is effective at fighting fluctuations in future planetary temperatures or merely effective at ceding expansive powers over every individual on Earth to international "authorities" and government bureaucrats.  Refusing to embrace socialized medicine is just evidence of racism against Barack Obama.  Refusing to elevate to the Oval Office a corrupt and congenital liar who used her position as secretary of state to enrich her own "charitable" foundation demonstrates how sexist most Americans are.  Adhering to the Constitution as written and respecting our Founding Fathers and founding documents are proof that America is both "patriarchal" and "white supremacist."  The left is no longer interested in debate — just pejorative labels.

(3) Becoming abusive to others who are different

"A basket of deplorables."  "Uneducated racists, clinging to guns and Bibles."  "The dogma lives loudly in you."  "Racism is wired into the American mind."  From the highest-ranking Democrats to the lowly foot soldiers looting and burning down small businesses throughout the country, violence and intimidation of Americans are now justified by labeling some Americans as unworthy of the protections of American law.  If you threaten strangers and destroy property in the name of Black Lives Matter or Antifa, then local Democrat prosecutors will make sure you never answer for your crimes.  If you exercise your Second Amendment right to protect the lives of your family and secure your property, those same Democrat prosecutors will threaten your liberty and future.  If you riot in the name of "justice," then you are performing a public service.  If you seek spiritual salvation by attending church or synagogue, then you are a public health threat.  When Democrats are in office, there are two tiers of justice in America, one for protecting Democrats and one for harassing Republicans.  Former attorney general Eric Holder aptly articulated this reality when he argued that the fight against Republicans is "not about principle" but about the "acquisition and use of power."

(4) Embracing conspiracy theories

When recently inaugurated President Trump tweeted that Obama had his "wires tapped" during the 2016 campaign, the mainstream media mocked and scorned him as a conspiracy theorist and loon.  They then spent four years trying to prove to the American people that Trump had conspired with Russia to "hack" the 2016 election and steal legitimate victory from Hillary Clinton.  "Russian collusion" has been a journalistic obsession, and it was all a lie.  There is, however, considerable evidence that Hillary Clinton and Barack Obama conspired with John Brennan at the CIA and James Comey at the FBI, along with numerous other high-ranking intelligence, law enforcement, and State Department personnel, to frame candidate and then president Trump as an agent of a hostile government.  All the American institutions that demand public respect have peddled baseless conspiracies for four years, while those few Americans who have defended President Trump from attack have been denigrated as kooks and charlatans.  

(5) Feeling persecuted

For Democrats, the most important person is the one who can claim highest victimhood.  Being gay is always better than being straight.  Being female is better than being male, but being transgender is better still.  The shade of a person's skin color is always more important than the content of that person's character.  Evidence of persecution is the noblest virtue for the left.  Unless you or your family has been a victim of socialism or communism — then you do not exist at all.  

(6) Distancing from old friends and changing appearance

When Antifa domestic terrorists dress from head to toe in black while throwing Molotov cocktails at police officers in upscale urban neighborhoods, can we all agree that the left has no interest in peace?  When MSNBC commentator Chris Hayes insists that the "most humane way ... to deal" with Republicans after the election is a "truth and reconciliation commission" similar to communist regimes' use of re-education camps, and neo-socialist Bill Kristol responds by promising that no reconciliation is possible with Trump-supporters, is it time to recognize that former Twitter CEO Dick Costolo's fantasies of violent revolution and political assassination should be taken seriously?  The Antifa and BLM riots this year have been the costliest in American history.  Members of Bernie Sanders's campaign openly talk about guillotines in the town square, and Hollywood celebrities celebrate the Chinese coronavirus as "God's gift to the left."  All of these threats come just three years after a single Democrat nearly succeeded in murdering an entire baseball field of Republican lawmakers.  These are not our old Democrat friends.

(7) Converting to a new religion

Leftism is dogmatic.  It demands fealty and does not tolerate dissent.  If you place personal liberty and free markets ahead of "Mother Earth," then you are a climate change "denier."  If you refuse to repent for the sins of past generations, kneel before BLM flags, and seek forgiveness for the color of your skin, then you are a "hater," a "supremacist," or "un-woke."  The Democrats abandoned working people for grievance culture, and every grievance must be used to divide Americans for good.  Mercy and forgiveness are gone; only hatred and intolerance are preached.

(8) Being secretive and reluctant to discuss activities

Will a President Biden pack the Supreme Court?  Help kill the filibuster in the Senate?  Continue to support Antifa and BLM rioting throughout the country?  Confiscate lawfully owned firearms?  Eliminate fracking and destroy high-paying coal and natural gas mining jobs?  Sacrifice American manufacturing so that communist China may prosper?  Remove America's embassy from Jerusalem, while strengthening Iran in the Middle East?  Biden won't say.  He's made only two promises this campaign: to raise taxes and to mandate the wearing of masks by executive decree.  Every other policy is a secret.

(9) Sympathetic to extremist ideologies and groups

If Republican-allied anarchist groups around the country were causing billions of dollars in property damage, assassinating police officers and political opponents, threatening suburban homeowners, and setting forest fires across the Pacific Northwest, every newspaper and news show in the United States would be highlighting the civil insurrection threatening the country.  Because all of this damage has been organized and committed by left-leaning groups, the news is actively censored both by traditional news corporations and the Silicon Valley tech lords regulating free speech today.

Democrats have become radicalized.  They have become violent.  And Facebook and Google and Twitter and CNN believe that it is in the best interest of the country to hide this truth from the American people.