The commitment extends the promise made by the Biden administration, which argues that corporations and the wealthy should bear a greater share of the tax burden.

Harris's pledge effectively rules out the possibility of embracing more progressive policies as a candidate, such as significantly expanding Social Security benefits, which would require raising taxes on a wider range of Americans. The tax pledge was a key aspect of Biden's appeal to working-class voters during his campaign, and Harris intends to keep this core commitment intact as she develops her own economic platform.

During a recent campaign rally in Wisconsin, Harris emphasized her belief in a future where every individual has the opportunity to not only get by, but to get ahead. She declared that building up the middle class would be a central goal of her presidency.

Democrats aim to highlight taxes as a contrasting point with former President Donald Trump, who passed a major tax cut package during his term and expressed support for further reducing the corporate tax rate. The 2017 tax law faced significant opposition at the time, and with major portions of that package up for renewal next year, Harris has echoed Biden's rhetoric by positioning herself as a champion for the middle class and criticizing Trump for advocating policies that primarily benefit the wealthy.

Harris has yet to present a detailed economic platform of her own since becoming the likely Democratic nominee, but she is expected to adopt much of Biden's broader agenda in the limited time leading up to the election. Biden focused on bolstering the working class throughout his term, with efforts to expand safety net programs and reduce healthcare costs. However, he faced challenges in winning over voters who blamed his agenda for rising prices and remained skeptical of his role in the post-Covid recovery.

Early polling suggests that Harris may encounter less opposition during her own presidential run. A recent poll conducted by the Democratic firm Blueprint shows Harris either ahead or on par with Trump in terms of voter trust on various economic issues. When asked about "fair taxes," Harris and Trump were tied in respondents' trust. Additionally, 40% of respondents indicated that Harris shares responsibility for Biden's pledge to raise taxes on the wealthy, a position that has been shown to be popular in prior polling.

While Harris advocated for more progressive economic proposals during her unsuccessful 2020 presidential campaign, including raising the corporate tax rate to 35 percent, Biden's current agenda calls for increasing it to 28 percent. Harris also previously suggested taxing certain stock trades and financial transactions. However, her campaign did not provide details on specific tax policies that would be part of her platform.

By maintaining Biden's pledge not to raise taxes on Americans earning under $400,000, Harris is signaling that she is unlikely to embrace more progressive ideas that would require increasing taxes on a broader segment of the population. One such proposal, led by Senator Bernie Sanders, aimed to boost Social Security benefits by $2,400 a year by applying a payroll tax to all earnings above $250,000 per year. Biden opted not to pursue this proposal due, in part, to its violation of his tax promise. Instead, he has advocated for strengthening the program's solvency through higher taxes on wealthy individuals.