For once, it would be nice to see Sen. Marco Rubio stand up as the independent leader he aspires to become. For once, the Florida Republican should hold his position rather than bow to pragmatic politics. Rubio can stick with his threat Thursday to vote against the Republican tax cut plan unless it is revised to increase benefits for the working poor, or he can reinforce his image as a senator who too often folds under pressure.Rubio wasn’t asking for the moon in the tax cut legislation. The Senate bill lowered the corporate tax rate from the current 35 percent to 20 percent, and he proposed setting the rate at 20.94 percent. Rubio wanted to use the freed up money to increase benefits for about 9 million low-income Americans who benefit from the child tax credit. The compromise legislation is expected to double the child tax credit to $2,000, but Rubio wanted to make the credit refundable against both income and payroll taxes. He warned of "problems’’ if the corporate tax rate was set above 20 percent and the savings were not used to expand the child tax credit.Republican leaders didn’t just ignore Rubio. They twisted the knife. The corporate tax rate was moved to 21 percent, and the money will pay for tax cuts for the wealthy instead of relief for low-income Americans. That should tell voters all they need to know about the Republicans’ real priorities and expose the hollow claims by President Donald Trump that this tax cut is aimed helping everyone.As Rubio tweeted Wednesday: "20.94% Corp. rate to pay for tax cut for working family making $40K was anti-growth but 21% to cut tax for couples making $1 million is fine?’’Apparently, although Trump hinted after the tax cut deal was announced that there is still room to address the issue. Republican Sen. Mike Lee of Utah, who joined Rubio in pushing the refundable child tax credit that was rejected, also held out hope of some movement before the final vote. Then Rubio issued his threat Thursday to vote against the bill unless it includes at least a smaller change than he initially proposed. We’ll see.In the Florida Legislature and then in U.S. Senate, Rubio has shown he cares more about being liked and being part of the Republican team than standing on principle. He helped negotiate a comprehensive immigration reform bill that passed the Senate four years ago with bipartisan support, than abandoned it when there was a conservative backlash. He took some of the worst abuse from Trump as a presidential candidate, then endorsed him before the general election and stuck with him even as the accusations of sexual harassment against Trump built. He said he would not run for re-election if he did not win the Republican nomination for president and changed his mind. Now he has pushed a reasonable expansion of the child tax credit that would benefit low-income Floridians and been embarrassed by the Republican leadership. He needs to remain firm in his threat to oppose the bill unless he is accommodated.Rubio easily won re-election last year and will not be on the ballot again until 2022. He remains one of the younger, camera-ready Republicans on the national stage. He has leverage, because Republicans control just 52 Senate seats. He can afford to tell Republican leaders he will vote against the tax cut legislation next week unless they include his child tax credit provisions. That should increase his influence in Washington and his standing among moderate voters who see the tax cuts as a giveaway to businesses and the wealthy.Finally, Rubio stood up for himself and for low-income Americans on Thursday. This time, he should not back down.