There are still basic questions Republicans need to answer about their massive tax plan

Since his campaign kicked off in 2015, President Donald Trump has remained consistent on a few policy positions. One of the most significant was his promise to deliver comprehensive tax reform, and it seems to be the issue to which he's devoting his attention now.

On Wednesday, Trump laid out his principles for that tax reform package in a speech kicking off a campaign to complete the task by the end of the year.

Despite the coming public tour, there's still a massive amount of behind-the-scenes work to be done to craft the actual plan.

According to multiple reports, Republicans have yet to craft a full-fledged piece of legislation, and public details from congressional leaders and White House have been sketchy at best. Trump himself did not get into specifics of the reform process in his speech in Missouri, instead opting for general principles that were a reheated version of other statements from the Trump White House.

Here's an overview of the biggest, but not all, the questions Republicans still need to answer about their tax plan:

• Are the tax cuts permanent or temporary? Passing permanent tax cuts are more politically difficult, since any bill adding to the deficit for more than 10 years can't be done through budget reconciliation. That would leave it open to a filibuster from Democrats in the Senate. That's why President George W. Bush opted for temporary cuts in 2001. Republicans have signaled they want something like the 1986 cuts under Ronald Reagan - which were permanent. House Speaker Paul Ryan has long argued for permanent cuts, but winning over any Senate Democrats, much less the eight required to bypass a filibuster, would be a tall task.
• What will be the proposed corporate rate? During an interview with the Financial Times, Gary Cohn, Trump's top economic adviser, did not commit to Trump's promised 15% corporate rate. He only said the White House wanted to get the rate "as low as possible." The rate could be fall to the mid-20s, a more modest decrease from the current federal rate of 35%.
• What will be the proposed rate for the repatriation tax? The Trump administration has floated a one-time rate around 10% to encourage US companies to bring cash back from overseas. That would be double the rate from the last repatriation in 2004. However, Cohn said no specific rate had been discussed during his FT interview.
• What deductions would be eliminated? Trump's team and most Republican leaders have only mentioned three deductions they plan to keep: on mortgage interest, charitable giving, and retirement contributions. Another question is what the plan would do with the deduction for carried interest, which lets managers of some private investment funds pay a lower rate. Overall, a reshaping of tax deductions could draw pushback from industries that benefit from a slew of exemptions - not to mention individuals who also benefit from tax breaks like the ability to deduct state and local taxes.
• What will the proposed income ranges be for new tax brackets? The Trump administration consistently references slimming the number of individual income tax brackets from seven to three. But they have not clarified what incomes would fall in each of those brackets.

The Trump administration and leading Republicans lawmakers have pushed to pass the tax reform bill by the end of the year.