On the day Boris Johnson signalled the end of one crisis — Covid — another one began in Ukraine. For once, he won’t mind: the timing of Russia’s intervention is good for him as he tries to hang on to his job. A return to “normal politics” as the Covid era drew to a close would leave Johnson much more exposed to the “Partygate” controversy threatening his premiership. Tory MPs say it is “unthinkable” the party will ditch its leader during an international crisis, whatever happens on “Partygate” — even though Johnson now has the unwelcome soubriquet of being the first prime minister to be interviewed under police caution. It looked as though Johnson’s luck and ability to emerge unscathed from dangerous scrapes had run out. But even some Tory critics concede privately that Ukraine has thrown him a lifeline. “He is still a lucky general after all,” one told me, “but I have to admit he is showing leadership on Ukraine.”

Some wobbly Tories, looking for any excuse to avoid another act of regicide, will find a plausible one in the current crisis. Johnson’s hasty lifting of Covid restrictions in England has delighted right-wing Tory MPs. “He’s finally doing what we have long told him to do,” one said. “It has made his position stronger.” “Partygate” still poses a grave threat. If Johnson gets another unwanted label and is fined, the number of Tory MPs demanding a vote of confidence in him might well pass the threshold of 54 needed to trigger such a vote. But his allies are very confident he would win it if Ukraine is dominating the headlines; cabinet ministers like Rishi Sunak would be less likely to break ranks and risk charges of disloyalty in a crisis. So Johnson’s critics should pause for thought and perhaps wait until after the May local elections for more ammunition.

However, Johnson will need to go much further on sanctions against Russia; the UK’s initial list didn’t match its threats and was seen as too feeble by many Tory MPs. He cannot afford to alienate them and also needs to dispel the damaging impression the Tories are shielding “Londongrad” and their Russian friends and donors. Ministers can’t say they were surprised by Vladimir Putin’s move; they have been predicting it for weeks and, unusually, made public US and UK intelligence. They insist they are forcing the pace on sanctions in talks with allies and are acting “in lockstep” to prevent Putin dividing his enemies. More sanctions will follow in the next few days.

In a media round today, Liz Truss, the foreign secretary, argued that the UK needed to keep some measures “in the locker” in case of a full Russian invasion of Ukraine. But she then undermined her case by warning that Putin was “hell-bent” on invading anyway. Ukraine also carries other risks for Johnson; sanctions could cost him and his party more public support if petrol and energy prices rise further during the cost-of-living crisis.

His strategy is to hug the Biden administration close to repair relations strained by the chaotic withdrawal from Afghanistan. If there are differences down the track on sanctions, the UK will side with the US rather than EU countries. Some tensions with Washington remain: Johnson’s foreign and security policy review last year aped America’s tilt to the Indo-Pacific to combat China even though the US urged the UK to focus on the big problem on its doorstep — Russia — rather than over-reach.

Successive governments have hoped to re-set relations with Moscow; that is not going to happen while Putin remains in charge. There will be no return to the days when Tony Blair played pool with Putin at his dacha or William Hague and Sergey Lavrov lubricated the relationship by downing several whiskies. A permanent change of strategy — including higher defence spending — will be needed, for the UK and EU. Truss has a timely platform on which to enhance her reputation and boost her chances of succeeding Johnson (although every PM is their own foreign secretary in an emergency). Admirers say Truss is showing steel but some Tory MPs were underwhelmed by her visit to Moscow and grate at what they call her “Margaret Thatcher tribute act.” Some judge her too robotic in media interviews to be a vote-winner.

In a leadership election, Truss’ opponents would move votes around between candidates to try keep her off the shortlist of two names from which grassroots Tory members choose the leader — a sign they know she might win. Ben Wallace, the defence secretary, is seen by Tory MPs as having a “good war”. But his hopes of becoming Nato’s next secretary general may have been scuppered by his suggestion EU countries appeased Putin, which went down badly in France and Germany. (However, Putin’s snub of Emmanuel Macron’s efforts to avert conflict left the French president looking naïve, even in some EU eyes).