With less than six weeks to go until Election Day, the political campaign season is reaching its peak. And that means lots of policy proposals and promises from the candidates. In recent weeks, we have seen a flurry of tax proposals from former President Donald Trump and Vice President Kamala Harris.

When thinking about tax policy, it is critically important to keep in mind that presidents cannot change the tax code through executive orders or other means. Only Congress can make changes to tax law. Proposals by presidential candidates are important, but they represent the starting point for a complicated negotiation that will take place on Capitol Hill.

Next year will feature one of the most consequential tax debates in years. That's because 2017's Tax Cuts and Jobs Act (TCJA) is set to expire at the end of 2025. Provisions of that law include lower individual income tax rates, a higher standard deduction, the $10,000 cap on the state and local tax deduction, the increased amount of assets that can be inherited without triggering the estate tax and dozens more—all would expire at the end of next year if Congress does not extend them. Everything would revert to what the law was prior to the TCJA.

But the expiring provisions are just the starting point for a complicated debate next year, with both presidential candidates proposing a variety of other changes to the tax code. The outcome of next year's debate will be heavily influenced by November's elections, which will determine the balance of power in Washington in 2025. A Republican sweep that results in unified control of the White House, the Senate and the House of Representatives, for example, would give Republicans the ability to shape a tax bill with their priorities. But if there is divided government next year, that would create a tricky dynamic requiring both parties to compromise.

Here is a look at what the candidates have proposed—and what the likelihood is of any of these proposals becoming law.

Trump has called for extending all of the tax cuts from the TCJA—a bill he signed into law during his years in office. Harris favors extending the tax cuts for lower- and middle-class taxpayers, but she would let the provisions expire for individuals earning more than $400,000 per year. Among other changes, that would result in the top individual income tax rate reverting to 39.6% from its current level of 37%. Whether to extend all, some or none of the expiring provisions is the launching point for next year's tax debate.

Currently, individuals can inherit an estate up to $13.61 million ($27.22 million for married couples) without triggering the estate tax. If the TCJA expires at the end of 2025, the exemption amount would revert to roughly $7 million beginning in 2026. Neither Harris nor Trump has made a specific pledge about the estate tax. On Capitol Hill, the estate tax is not a purely partisan issue—there are lawmakers from both sides of the aisle who are concerned about the potential abrupt drop in the size of the estates that would be affected. A compromise that reduces the exemption amount from its current level but does not let it revert to its pre-2017 level is not out of the question.

The TCJA imposed a cap of $10,000 on the amount of state and local taxes that an individual can claim on a tax return. If the TCJA expires, there will be no cap beginning in 2026. Trump, who signed the cap into law as part of the original TCJA, recently said that he would restore the SALT deduction without a cap, though he provided no other details. Harris plans to preserve the cap. Some on Capitol Hill have floated doubling the cap for married couples as a possible alternative approach. The deduction has an unusual dynamic in Congress, where lifting the cap is a top priority for a bipartisan group of lawmakers who represent high-tax states like California, New Jersey and New York. But for many lawmakers who represent other parts of the country, the issue is not a priority at all, making it a particularly unpredictable outcome to forecast.

The current top capital gains rate of 20% is not part of the expiring provisions. Harris recently outlined her proposal for taxing capital gains of wealthier filers, a proposal that was notable for how it broke with President Joe Biden's long-standing view. Biden has long argued that capital gains above $1 million in income should be taxed as ordinary income. He also has called for an increase in the Net Investment Income Tax (NIIT), the 3.8% surtax on investment gains for wealthier filers, to 5%. That could create a top capital gains tax rate of 44.6%. Harris, however, has called for a top capital gains rate of 28%, plus a 5% NIIT, for an all-in top rate of 33% for filers with income above $1 million. The plan is likely to run into strong opposition from Republicans on Capitol Hill, giving it a low probability of success in a divided Congress in 2025. Trump has given no indication that he is contemplating any changes to the current rate.

Harris has endorsed a Biden proposal to create a "billionaire's tax," which would impose a minimum tax rate on individuals with more than $100 million in assets. It would require taxing unrealized gains for assets above that level.

We think this is highly unlikely to happen. On Capitol Hill, Democrats are not unified around the idea of taxing unrealized gains, and Republicans are uniformly against it, meaning it is unlikely it could win majority support in either the House or the Senate. Moreover, the proposal has numerous operational questions and may not even be constitutional.

Trump has called for lowering the corporate tax rate to 15% from 21% for companies who make their products entirely in the United States. Harris, on the other hand, has called for an increase of the corporate tax rate to 28%. The current rate is not part of the expiring provisions and it's not clear how much appetite there is on Capitol Hill for changing it.

The former president has proposed a series of tax changes on the campaign trail, including eliminating the tax on tip income, ending the taxation of Social Security benefits and eliminating taxes on overtime hours worked. These proposals have not been fully fleshed out, but early analyses by economists and tax experts have raised questions about how they would work and the impact they would have on the federal deficit and the national debt. That doesn't mean they won't be part of the policy debate in 2025, but it's too early to tell whether they will pick up significant momentum.

The vice president has also made a series of proposals during the campaign, including an expanded child tax credit for newborns, a new tax incentive for first-time homebuyers and increasing the tax deduction for small-business start-up costs. These have strong support among Democrats, but whether they pick up momentum in next year's debate will depend on how Democrats fare in the November election. Experts have pointed out that Harris's proposals, like Trump's, could also have a significant impact on the federal deficit and national debt.

A promise to reduce taxes has been a feature of most presidential campaigns for decades. But taxes can only be adjusted by Congress. That means the proposals made by candidates represent the starting point for debate, nothing more.

There is broad expectation that 2025 will see the most significant debate over tax policy in nearly a decade. But it's far too early to know exactly how that will play out and it is a virtual certainty that anything Congress does end up approving next year will look very different from the proposals that are out now. Investors should be cautious about making any decisions now based on possible changes to tax law in the future.