WASHINGTON (AP) — The Latest on the Republican tax overhaul (all times local):

A group of Republican senators appears optimistic after meeting with President Donald Trump about a GOP-led tax plan.

Texas Sen. John Cornyn says the current plan is to vote on the tax bill this week on the Senate floor. He says the Senate bill has made some “substantial improvements” from the House version of the bill, but they will sort out those differences in a joint House-Senate conference committee.

In addition, a Senate Republican says GOP leaders are working on a potential revenue “backstop” in case the party’s tax cut legislation fails to produce hoped-for levels of growth and tax receipts.

Oklahoma Sen. James Lankford said he and other Republicans are working on “just-in-case options” to add to the measure during Senate floor debate this week. He appears to be talking about a mechanism that could automatically force tax rates back up if revenues fall short.

Lankford cited the experience of states like Oklahoma and Kansas, which are now facing big shortfalls after aggressively cutting taxes. He added that lawmakers “should build in the ‘what if?’ What if this doesn’t work?”

The Republican tax plan would cut corporate and personal taxes by $1.5 trillion over the coming decade. Lawmakers are working on ways to pay for those cuts.

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10:25 a.m.

President Donald Trump says changes are to the Republican tax bill are coming, as he looks to win over holdout GOP senators in an effort to pass the package by the end of the year.

In a Monday morning tweet, the president says, “With just a few changes, some mathematical, the middle class and job producers can get even more in actual dollars and savings.”

Trump is suggesting openness to making unspecified changes to the way millions of “pass-through” businesses are taxed, a sticking point for some lawmakers.

Trump is set to meet Monday afternoon with five members of the Senate Finance Committee, all of whom are on board with the GOP plan. He will travel to Capitol Hill Tuesday to personally lobby Republican senators.