Julian Zelizer is a professor of history and public affairs at Princeton University, and author, with Kevin Kruse, of the new book "Fault Lines: A History of the United States Since 1974." Michael Zeldin, a CNN legal analyst, served as Deputy Independent Counsel, and later as Independent Counsel, in the investigation into allegations that the administration of George H. W. Bush violated the privacy rights of candidate Bill Clinton in the 1992 presidential campaign. He also served as a Special Counsel to Robert Mueller in the Department of Justice. The opinions expressed in this commentary are those of the authors; view more opinion articles on CNN.

(CNN) President Donald Trump has not been able to persuade Congress that US national security requires the building of a wall at our southern border. If, however, a national emergency really exists, as the President insists, then he should take his case directly to the American people and look to other ways to pay for a wall -- ways that do not require the use of pre-existing taxpayer dollars.

Our suggestion is that the President propose issuing "wall bonds," or government-issued debt securities, to fund the wall. After all, the best measure of support for a government program is whether the public is willing to pay for the program.

The idea of selling government bonds to fund a government program is not new. In the first half of the 20th century, presidents were able to rally the public to pay for national emergency programs. During World War I and World War II, President Woodrow Wilson and President Franklin Roosevelt each undertook massive initiatives to raise the money that was needed to mobilize the troops through the issuance of bonds and imposition of higher taxes.

President Wilson's Secretary of the Treasury, William McAdoo, sold "Liberty Loans." And under President Roosevelt, Treasury Secretary Henry Morgenthau launched a major campaign to sell war bonds and to persuade voters that higher taxes were necessary. "Taxes to Beat the Axis," Treasury said.

Millions of Americans bought war bonds during both campaigns, with many convinced by the Presidents that the mission was worthwhile. "Save to Win" read the cover of a $25 war bond that low-income Americans could invest in by purchasing 25 cent stamps. And "The Treasury Star Parade," the Treasury's variety show, employed musical stars to promote war bonds.

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