(CNN) The news just keeps on getting better for Vladimir Putin.

On either side of the Atlantic, the United States and Britain, the two great English-speaking democracies that orchestrated Moscow's defeat in the Cold War, are undergoing simultaneous political breakdowns.

And the Russian leader may have had a hand in triggering the turmoil.

In London, Theresa May on Tuesday suffered the worst defeat in the modern parliamentary era by a prime minister, as lawmakers shot down her Brexit deal with the European Union by a staggering 432 votes to 202.

The United States, meanwhile, remains locked in its longest-ever government shutdown, which is now entering its 26th day , is nowhere near ending and is the culmination of two years of whirling political chaos sparked by President Donald Trump.

It's hard to believe that two such robust democracies, long seen by the rest of the world as beacons of stability, have dissolved into such bitter civic dysfunction and seem unmoored from their previous governing realities.

The political self-recrimination is a far cry from the days when President Franklin Roosevelt and Prime Minister Winston Churchill and President Ronald Reagan and Prime Minister Margaret Thatcher bonded to face down totalitarian threats to Western, liberal democracy.

Now the threat to the political solidity of the West is coming partly from the inside, from a fractured political consensus that makes it impossible to address vital questions like Britain's relations with Europe and immigration in the US.

Supporters of Trump in the US and Brexit in Britain see their revolts as uprisings against distant or unaccountable leaders who no longer represent them or share their values. But the disruption that some see as a reinvention of democracy is viewed by skeptics as deeply corrosive to the international political architecture that has prevailed for over 70 years.

The meltdown in Britain has some foreign investors wanting to know if Britain has "lost its mind," said Tina Fordham, chief global political analyst for Citigroup.

"Even though ... I've been writing about magical thinking in politics and anticipating all of this -- I too am astonished that reason is not prevailing," Fordham told CNN International's Julia Chatterley on Tuesday.

Common political forces

While the political stalemates in London and Washington are not an exact match, some common factors combined to lay siege to what have long been two of the world's most resilient democracies.

The allies are experiencing the reverberations of populist revolts that erupted in 2016 -- in the Brexit vote and the election of Trump -- and are now slamming into legislatures and breeding division and stasis.

The result is that Britain and the United States are all but ungovernable on the most important questions that confront both nations.

That's music to Putin's ears.

The Russian leader has made disrupting liberal democracies a core principle of his near two-decade rule, as he seeks to avenge the fall of the Soviet empire, which he experienced as a heartbroken KGB agent in East Germany.

Over the last five years, Putin has defied Western scorn about Russia's frayed economic power and made the best of a bad hand, working to re-establish influence in the former Soviet orbit.

He has seized Crimea from Ukraine and restored Moscow's former political beachhead in the Middle East.

In the last two years, Putin has had a witting, or unwitting, ally in Trump, whose attacks on NATO and US allies and decision to pull US troops out of Syria played into Russia's goals.

Whether the political distemper in the West was sown by a Russian intelligence operation masterminded by Putin may not matter because he is making a belated effort at winning the peace after the end of the Cold War.

His success is adding urgency to the question that special counsel Robert Mueller has spent nearly two years investigating -- whether Trump's campaign cooperated with Moscow to influence the election in 2016.

In another win for Putin, America is tying itself in knots in a surreal national debate over whether Trump -- who incidentally is a vocal supporter of Brexit -- is working on behalf of Russia, following a bombshell New York Times report.

"This is why it is so not normal to have to ask, well, whose side is the President on? Russia's side or our side?" Sen. Mazie Hirono, D-Hawaii, asked on CNN's "New Day" on Tuesday.

"It is the accumulation of what seem like unusual, head-scratching, disparate kinds of utterances from him, when you start to see a pattern, when he basically spouts Putin's lines."

Trump's mysteriously cozy relationship with the Russian leader was on display at the Helsinki summit last year. He also often seems to adopt a Putinesque worldview despite his claims that no President has been tougher on Russia than he is.

But on Monday, adding to an unreal atmosphere in Washington, Trump had to take the extraordinary step of saying he was not working for Russia.

Populist in chief

Trump's enlistment of rural, conservative voters against metropolitan elites echoes the arguments of leaders orchestrating Britain's exit from Europe.

Now, in both nations, the unwillingness of rebels to dilute the purity of their goals is causing gridlock and resistance in Congress and in Parliament.

In the United States, Trump is mounting a defiant stand on his border wall, which triggered the partial government shutdown. It's just as important for Trump to keep faith with voters with whom he bonded over the wall as it is for Brexiteers to honor the 2016 referendum vote to leave the EU. This is the case even though both aspirations, which have taken on mystical properties, are becoming more elusive.

With the US President not bending and with Democrats adamant they won't fold, 800,000 government workers could be without pay for days to come, and halfhearted attempts to break the partisan deadlock have failed.

Britain, meanwhile, is mired in the worst political crisis since World War II. While a slim majority voted to leave the EU, there is no consensus on how to do it, and about half the country still wants to stay in the bloc.

The voluble Trump and the plodding May could not be more different in personality and political style. The Prime Minister is a creature of the Conservative Party establishment and spent years climbing to the top.

Trump never went native in Washington. He's still the ringleader of a populist movement that sent him to power in a stunning political upset.

But they are both leaders who once set on a course are loath to turn back, and often speak in slogans like "Build the wall" and "Brexit means Brexit," which sound good but don't help them follow through on their goals.

While persistence can be a strength, it can also backfire.

Trump has been saying the same thing for days -- that Democrats are soft on the border and need to capitulate. But he's failed to rally a coalition of Americans behind his border wall. Effectively he's led the Republican Party into a political dead end.

May repeatedly insists that her rejected deal is the only way to honor the 2016 referendum, right up until its massive defeat.

But she has failed to build public support for her approach. If anything, she's more locked into a failed political position than Trump is on the shutdown.

And the deeper the trans-Atlantic dysfunction gets, the better it is for Putin.