BERLIN (Reuters) - German Finance Minister Olaf Scholz, a Social Democrat, has threatened to make pensions a central theme in the next national elections in 2021 unless Chancellor Angela Merkel’s conservatives agree to guarantee pension levels until 2040.

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Scholz told the Bild am Sonntag newspaper that securing stable pension levels was a top priority for his party, which has seen its political support drop to historic lows since the 2017 election.

The ruling coalition has agreed only to keep pensions stable until 2025, but Scholz said his party was pressing for guarantees that would continue through the 2030s.

Doing so, he said, was the best insurance Germany could muster to prevent further increases in support for populist parties.

“Globalization and digitalisation create wealth, but they are also changing our world at a rapid pace. Our citizens expect, appropriately, that we do everything possible to ensure that they can still live well,” he told the newspaper.

“Stable pensions will prevent a German Trump,” he said, in a reference to the anti-establishment wave that swept U.S. President Donald Trump into power in 2016.

If Merkel’s conservative bloc refused to agree to keep pensions stable through to 2040, the issue would become the focus of a major political fight, Scholz said.

“Then the citizens will decide this issue with their ballots,” he said.

Germany faces its next national election in 2021, but several states - including Bavaria - go to the polls in the interim.

A new poll conducted for the Bild am Sonntag showed that the conservatives had lost one percentage point to poll at 30 percent, while the SPD was steady at 17 percent. That means that if Germany voted again tomorrow, the grand coalition would not have enough support to govern.

The poll, conducted by the Emnid institute, showed the anti-immigration Alternative for Germany (AfD) party gaining one point to 15 percent, and the pro-business Free Democrats adding one point to poll at 9 percent.