Consider the following example, which demonstrates why Mrs. Clinton’s plan misses the mark.

When stock vests, an executive recognizes ordinary income for the fair-market value of the shares, taking that amount as the tax basis in the shares.

Suppose an executive received 50,000 shares of restricted stock in 2012, when the stock was worth $1 million, or $20 a share. Suppose the restrictions lapse in 2016 when the stock is worth $2 million, or $40 a share. Under either current law or Mrs. Clinton’s plan, the executive would recognize $2 million of ordinary income and pay about $800,000 in income taxes. The executive would then have a basis in the shares of $2 million. This result does not depend on whether the executive sells the stock immediately or holds on to it after it vests.

Under Mrs. Clinton’s proposal, if the executive sold the stock 18 months later for $42 a share, he or she would recognize $100,000 of short-term capital gain, paying tax of about $40,000. Under current law, the executive would pay tax of $20,000.

But raising the rate on tax gains also raises the value of tax losses. If the stock price declined to $38 a share, the executive would recognize a short-term capital loss of $100,000, worth about $40,000. Under current law, he or she would have a long-term capital loss of $100,000, worth about $20,000.

And whatever happens to the stock price after the stock vests, the amount of tax is likely to be small compared with the tax on the stock award itself, which is taxed at ordinary income rates. As a general matter, the stock price of a publicly traded company is about as likely to go down as it is up, and so broadly speaking, corporate executives care more about the top rate on ordinary income than the top rate on capital gains.

Executives of start-ups and other privately held firms often make an election under section 83(b) of the tax code that results in stock appreciation being taxed at capital gains rates. Those executives would not be affected much by Mrs. Clinton’s proposal. They typically hold shares for longer periods, and, as a general matter, do not engage in the sort of short-term earnings management that Mrs. Clinton is focusing on.

A better approach would be to pressure firms to change executive compensation practices. I would suggest an overhaul of Section 162(m), which disallows corporate deductions for pay above $1 million unless it is based on meeting performance goals. Instead, Section 162(m) could be rewritten to allow a deduction for compensation paid to any employee in excess of $1 million only if the compensation is paid in cash, deferred for at least five years and unsecured (meaning that if the company goes bankrupt, the executive would not have a priority over other creditors). This approach would encourage corporate executives to act more like long-term bondholders and obsess less about short-term stock price movements.