The French president, Emmanuel Macron, is expected to launch his campaign for re-election this week in a race shaken by the war in Ukraine, with key candidates under attack over previous pro-Russia stances. Macron has left the official declaration of his candidacy to the last minute because of the war, but he must make a move before the 4 March deadline to register. “This war will last,” Macron warned as he cut short his visit to the Paris agricultural fair this weekend, which is usually one of the key fixtures of the political calendar. There are only six weeks until the first-round presidential vote on 10 April, with the war in Ukraine the biggest international crisis to have hit a French presidential race in decades. Polls show Macron can win a second term, but there is a rise in support for far-right identity politics in France, with two far-right candidates in the race: Marine Le Pen, who is running for a third time, and a newcomer, the TV pundit Éric Zemmour, who has convictions for incitement to racial hatred. Both Le Pen and Zemmour have been challenged over their previous pro-Kremlin stances and have been criticised for backpedalling after the Russian invasion. Le Pen, who Macron defeated with 66% of the votes in the presidential final in 2017, is in the lead position to face him again in the final round, according to polls. But Le Pen accepted a loan from a Russian bank in 2014 to fund her 2017 campaign during which she paid a high-profile visit to Putin, praising him. Since the Russian invasion, she has been criticised by other candidates for her earlier pro-Russia stance. In a statement, she called for “an immediate end to military operations” and said the invasion must be “condemned without ambiguity”. Zemmour, who had downplayed the risk of war and suggested last year that Putin was not an aggressor, but was instead being treated aggressively by the international community, said he “condemned without reservation” what he called Russia’s “unjustifiable” military intervention. Jean-Luc Mélenchon, the hard-left presidential candidate, has in recent days pulled ahead of other candidates on the divided left, according to polls. He condemned the Russian invasion “as an extremely serious act of war” and “an unacceptable violation of the principles of international law”. But he was forced to defend his long-term position of France staying “non-aligned”, insisting in a live TV interview: “I have never supported Vladimir Putin, ever.” The Russian invasion has become a key issue for political debate. Clément Beaune, the Europe minister and Macron ally, said Le Pen, Zemmour and Mélenchon were “prisoners of their own contradictions and backpedalling” and were neither “coherent nor credible”. Valérie Pécresse, who is standing for Nicolas Sarkozy’s Les Républicains party, said at a rally this weekend that the war in Ukraine was “a turning point” in the French presidential campaign because it had allowed “masks to fall” and revealed what she called shameful geopolitical positions of rival candidates. She criticised Zemmour, Le Pen and Mélenchon and called them “discredited”. But Pécresse, who has slipped in the polls, had been under pressure over the stance of Sarkozy’s former prime minister, François Fillon. On the board of two large Russian energy firms, Fillon had been criticised for saying, just as Russia launched its invasion of Ukraine, that “the west won’t listen” to Moscow’s demands concerning Nato. Fillon announced in the Journal du Dimanche on Sunday that he would quit the petrochemical firm Sibur and oil company Zarubezhneft.