WASHINGTON—Republicans are scaling back their ambitions to overhaul safety-net programs and dismantle the Affordable Care Act following President Donald Trump’s weekend retreat with GOP leaders, due to concerns they can’t muster enough support ahead of the 2018 midterm elections.

Instead, Republican lawmakers are likely to embrace a slimmed-down agenda focused on the basics, including funding the government, raising the government debt limit and striking a deal on immigration, according to GOP lawmakers and aides.

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