(CNN) The House is expected to vote Thursday on the most robust piece of immigration legislation to come to the House floor in more than a decade, a dramatic showdown that will test some conservatives' loyalty to President Donald Trump.

After years of almost-votes, countless working groups and false alarms, the significance isn't lost on Republicans. House members will vote on a bill that funds Trump's signature campaign promise of a border wall and provides a path to citizenship for individuals who were brought to the US illegally as children by their parents, all happening under a retiring speaker who once vowed to conservatives he would not touch immigration as long as Barack Obama was President.

Whether the bill passes will be up to some of Trump's closest conservative allies in Congress, a direct reflection of whether members believe they can trust him to spend his own political capital and shield them from any backlash they may face from the base.

"Some of the members want to make sure the President is very visible in his support for both bills this week," said Rep. Mark Walker of North Carolina, the chairman of the conservative Republican Study Committee. "They want to see it constantly as we move forward."

Immigration as an issue -- unlike tax revisions, gun laws or efforts to reduce the debt -- has long divided Republicans more than it has united them, a side effect of regional, cultural and political differences that aren't easily remedied and have grown only more stark over time.

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