BERLIN — To draw Angela Merkel out of her shell, the German chancellor's main challenger Martin Schulz is taking a big gamble: He's playing the refugee card.

But not everyone, even in the ranks of his own Social Democrats, is convinced it's a good idea.

Schulz is heading to Italy on Thursday, seeking to present himself as a high-level fixer with a plan to deal with the rising number of migrants once again heading for Europe's shores. The trip comes after the former European Parliament president sounded the alarm over the issue in a series of interviews at the weekend, just two months before Germany's parliamentary election.

“In 2015, more than one million refugees arrived in Germany — mostly uncontrolled,” Schulz told Bild am Sonntag newspaper, using a higher number than the roughly 890,000 asylum-seekers who registered in Germany that year.

Referring to Merkel’s controversial decision in 2015 to grant safe passage to migrants stranded in Hungary, Schulz noted this had been done "without the agreement of our partners in Europe. If we don’t act now, this situation threatens to repeat itself.”

The strategy has an obvious advantage for Schulz — it reminds voters of Merkel's handling of the refugee crisis, which badly dented her popularity. But the chancellor has since staged a strong recovery, with her conservative bloc holding a double-digit lead over Schulz's Social Democrats (SPD). And there seems little chance voters who saw the conservative chancellor as too soft on migration would turn to the center-left SPD instead.

Substance versus slogans

Faced with Merkel's popularity, however, Schulz and his aides have decided they need to try to draw her out of her aloof approach to the campaign so far. They have drawn up a multi-part strategy to attack the veteran chancellor on various flanks, according to a high-ranking SPD official, who was involved in mapping out the plan and spoke to POLITICO on condition of anonymity.

So far, Merkel has primarily run on promising voters "security and prosperity for everyone," while refraining from providing too many details. It has paid off so far for the long-time chancellor, who knows that voters in her wealthy country value few things as much as stability.

The SPD's answer is to paint Merkel's campaign as devoid of content while presenting its own concrete proposals.

As part of that strategy, the SPD released its concepts for Germany's retirement pension system and tax reforms over the last couple of weeks. Last weekend, the time had come for the party to present its plan on migration, the official said.

Other watchers of German politics, however, were unimpressed.

It wasn’t just that Schulz, whose campaign has repeatedly been criticized for being disorganized, used a flawed number to support his claim or that Merkel is on vacation, making it easy for her to simply ignore the attack.

Immediately after Schulz spoke out, commentators were quick to note that the SPD itself — the junior partner in Merkel’s ruling coalition — backed the chancellor's decisions back in 2015.

At the same time, many of Schulz's proposals for dealing with the refugee crisis — demanding more solidarity from all EU member countries in the distribution of refugees, speeding up deportations to safe countries of origin in Africa, and opening up more legal ways to migrate to Europe — sounded similar to what Merkel herself has been advocating over the last two years.

Hubertus Heil, the SPD's secretary-general, insisted the party was not raising the issue to try to distinguish itself from Merkel's camp.

"It's important to speak about the big questions of the moment," he told reporters Monday. "We can't pretend that this issue has been solved just because there's a national election on September 24."

His underlying message: Unlike Merkel, Schulz is addressing pressing issues before they become acute.

When Schulz travels to Italy later this week to meet Prime Minister Paolo Gentiloni in Rome and visit a refugee center in Sicily, this will produce images to reinforce the SPD's message, party officials hope.

Far right spots opportunity

Not everyone's buying it — including some among Schulz's own SPD.

In the party's group in the German parliament, Schulz' move caused irritation, officials said Monday, warning that instead of harming Merkel, it could end up strengthening the far-right Alternative for Germany (AfD).

One SPD official in the parliament, speaking on condition of anonymity, said it might have been “correct in substance” to draw attention to an emerging refugee crisis in Italy. “But I don’t get where this is supposed to lead [in the campaign]," he added. "This will only help the AfD."

The AfD was founded in 2013 as a protest party against the euro but took an increasingly anti-immigrant stance during the refugee crisis and managed to climb up to 15 percent in opinion polls.

Since then, with the issue of refugees disappearing from major headlines, the party has fallen back to around 8 percent.

On Monday, it didn’t take long for the populists to seize on Schulz's comments.

“Schulz has realized that it won’t be possible until September 24 to continue pretending that illegal mass migration to Europe doesn't exist,” said AfD’s deputy leader Alexander Gauland.

He argued Schulz could not offer answers to the refugee crisis when the SPD had been part of the problem.

“It was his comrades in the parliament and government who contributed to creating this catastrophic situation in Germany and Europe,” Gauland said.