BERLIN: Chancellor Angela Merkel's Bavarian conservative allies threw their weight Monday behind her quest for a fourth term, putting aside a long-running argument over her migrant policies as Germany prepares for a national election in September. The show of conservative unity at a meeting in Munich came as Merkel's rivals, the center-left Social Democrats, are enjoying a strong poll boost from their surprise nomination as her challenger of Martin Schulz, the former president of the European Parliament and a relatively fresh face in national politics. Bavaria's Christian Social Union has dominated its southeastern state for decades and is traditionally an important source of national election votes for the conservative bloc led by Merkel's Christian Democratic Union. Their sometimes-awkward alliance has been frayed since late 2015, with CSU leader and Bavarian governor Horst Seehofer becoming one of the most prominent domestic critics of Merkel's welcoming approach to migrants. A year ago, he was threatening Merkel's federal government with a lawsuit if it didn't take measures to further secure the German border and reduce the influx of asylum-seekers, a threat never carried through. More recently, the CSU raised doubts about whether the parties would campaign together. Merkel, Germany's leader since 2005, announced her candidacy in November. 'We are going into this election campaign together,' Seehofer said Monday. Under Merkel, he said, 'Germany is an island of stability.' The conservatives have agreed to move past their dispute and focus on the Sept. 24 election, although they still disagree on a CSU demand for an annual cap of 200,000 on the number of refugees allowed into Germany. Germany saw 890,000 asylum-seekers arrive in 2015 and 280,000 last year, many of those before the Balkan migrant route was effectively shut by border closures from other nations. In practice, much has changed since the peak of the migrant influx in 2015. While Merkel insists that Germany will continue to take in people who genuinely need protection, her government has toughened asylum rules and declared several countries 'safe,' meaning people from there can't expect to get refuge. Merkel was also a driving force behind an agreement between the European Union and Turkey to stem the flow of migrants and favors a similar deal with countries in North Africa. She has also called for a 'national effort' to ensure that rejected asylum-seekers leave Germany. The CDU and CSU currently govern Germany in a 'grand coalition' of the country's biggest parties with the Social Democrats, who nominated Schulz as Merkel's challenger two weeks ago. Both sides want to end that alliance. Several polls over the past week have shown the Social Democrats' previously moribund support picking up significantly, cutting into what was a very large conservative lead. It's far from certain, however, whether their momentum will last. The conservatives also face a challenge on the right from the nationalist Alternative for Germany party, which hopes to enter the national parliament for the first time after assailing Merkel's welcome for migrants.