Stock markets in the United States rose Tuesday morning, buoyed by optimism over far-reaching tax changes that President Trump’s administration is expected to propose in the coming days.

The Nasdaq composite index rose above 6,000 for the first time, while the Dow Jones industrial average and the Standard & Poor’s 500-stock index also opened sharply higher.

The gains were also driven by stronger-than-expected corporate earnings, as well as the results of the first round of France’s presidential election.

Stock markets have risen steadily in the months since Mr. Trump’s election, based on expectations of deregulation and business-friendly policies supporting economic growth.

Although tax overhaul was a major plank of the president’s campaign, that effort has taken a back seat in recent months over concerns it would expand the budget deficit and face congressional backlash.

In recent days, however, Mr. Trump has instructed his staff to focus on cutting the corporate tax rate to 15 percent as part of tax changes to be unveiled this week, according to people with knowledge of his plans. He has apparently said they should do so even if it meant forgoing his promise to curb deficits.

In morning trading on Tuesday, the Nasdaq composite index rose as much as 0.6 percent, to a high of 6,022.58. The Dow Jones industrial average gained 1.2 percent, while the S.&P. 500 advanced 0.7 percent. The yield on American 10-year Treasury bonds also rose, indicating bond investors anticipate stronger economic growth and inflation.