With Germany's Social Democrats (SPD) slumping in the polls, its leader called on the party to take on Chancellor Angela Merkel in a September election on a program of investment, social justice and a stronger Europe. The chances of denying Merkel a fourth term look slim for the SPD, who are currently junior partners in her right-left coalition, but some are hoping for a resurgence like that staged by Britain's Labour party under Jeremy Corbyn in a June 8 vote. The SPD has squandered gains of around 10 points made soon after Martin Schulz, a former president of the European Parliament, was nominated party leader in late January. An Emnid poll on Sunday showed Merkel's conservative Christian Democrats widening their lead to 15 points. Schulz, addressing party members gathered to agree a manifesto for the Sept. 24 election, focused on free education, reducing the tax burden on low- and middle-income Germans, investing in infrastructure and fostering a united Europe. "We are living in a time of upheaval. Now Europe must be founded again," said Schulz, stressing the importance of human rights, disarmament and investing in digital infrastructure. "That is the task for Europe, the task for the SPD," he said in a combative, 80-minute speech to about 600 delegates and 5,000 guests. "I have fought for these ideas through my life. It is worth going onto the streets for these ideas, to make sure the next government is a Social Democratic one which will make them a reality. For this idea it is worth fighting with a passionate heart," he said to applause. He also accused Merkel of failing to stand up against US President Donald Trump and sharply criticized Turkish President Tayyip Erdogan, saying he should release jailed journalists. Schulz also rejected big increases in defense spending, in particular on weapons. The SPD has lost confidence after losing power in two state elections and failing to win in a third this year. To have any chance of winning in September, the center-left SPD needs to mobilize traditional supporters, who have either not voted or shifted allegiance in the past few years. As the number of refugees arriving in Germany has fallen sharply, many voters have forgiven Merkel for her open-door migrant policy and see her as a safe pair of hands, especially on the international stage. Earlier on Sunday, ex-Chancellor Gerhard Schroeder, the last Social Democrat to lead Germany, told delegates the party could still win, reminding them of the SPD's fightback to run Merkel close in the 2005 election — the last one he fought. "This is our chance. If we mobilize all our forces in the next few weeks, we can succeed in making the SPD the biggest party," he said to loud cheers. Schroeder said the SPD made up more than 20 points in the polls in a few weeks in 2005 and ended up only one percentage point short of Merkel's conservatives. "Nothing has been decided yet," said Schroeder, 73, who was chancellor from 1998 to 2005. A third of voters make up their minds on election day or shortly before, he added, calling for party members to fight for their cause with passion. — Reuters