He drew widespread attention over objections to Rex Tillerson but then cast a key vote that allowed the Exxon Mobil CEO to become Secretary of State.

He made a highly-publicized push to make the tax bill better for working class families but even in failure, supported the overall legislation.

Now Sen. Marco Rubio is laying down another marker.

As the tax package goes to conference, he's called on colleagues to improve the child tax credit, again positioning himself as a champion of the little guy.

"I remain surprised that there is not more consensus to support the reality that we do need to do more to help working people in the this country and the child tax credit is one of the best tools to do it," the Florida Republican said Wednesday on the Senate floor. "And I sure hope that what comes back from that conference committee is as good or better than what we've put out from the Senate because if it's worse, there's going to be problems I imagine."

Does that mean he would oppose the final version of the bill?

Rubio isn't saying. It's likely he will side with the party — as he did with Tillerson and last week. His words Wednesday make clear that he would accept what the Senate already passed.

Instead of voting for the deal last week, Rubio and Sen. Mike Lee could have stood their ground and demanded concessions, not unlike what Sen. Jeff Flake did. But Rubio chose not to upset a hurried, determined process. Doing so would have angered influential figures such as the Koch Brothers and President Trump.

Rubio's efforts on the child tax credit were not without success. Pressure got Senate tax writers to bump the credit to $2,000, from $1,650. But the benefits for lower wage earners — the firefighters, construction worker and teachers Rubio spoke of — were meager.

The Senate yesterday approved a motion from Rubio calling on Senate conference members to ensure $2,000 remains the minimum as the House called for $1,600. He also wants negotiators to "ensure that the final bill expands benefits so that more low-income, low-wage parents, workers, will be able to benefit from the child tax credit."

As Rubio conceded, those provisions wouldn't make a huge deal for some families but it would be better than the current situation.

There is potential, in theory. President Trump last week opened the door to setting the corporate tax rate somewhat higher than 20 percent. But lawmakers are eyeing that room to pay for other things, including more relief for people in high-tax states such as New York and California and more benefits for business.