Congress may be on the verge of striking a long-awaited deal on immigration reform when it returns to work after the Memorial Day recess, but lawmakers caution that a final compromise is far from assured.

Democratic Senate leaders pledge to take up a bipartisan compromise authored by the Gang of Eight senators in June. But a separate bipartisan group is crafting a House version of the bill that House Minority Leader Nancy Pelosi, D-Calif., said could be merged with the Senate version before Congress’ summer recess in August.