Phyllis Schlafly endorses Republican presidential candidate Donald Trump in St. Louis on March 11. (Seth Perlman/Associated Press)

Donald T. Critchlow, director of the Center for Political Thought and Leadership at Arizona State University, is author of “Phyllis Schlafly and Grassroots Conservatism” and “Future Right: Forging a a New Republican Majority.”

Phyllis Schlafly may be best remembered for the decisive role she played in defeating the Equal Rights Amendment in the late 1970s. Yet her more enduring legacy — reflected in the success of her chosen candidate, Donald Trump, in winning the 2016 Republican presidential nomination — was shaping and fueling the rise of the populist right. As much as Trump might seem to differ from Barry Goldwater, the candidate who originally helped propel Schlafly to prominence, Schlafly’s support of Goldwater in 1964 and Trump in 2016 share a common thread in her revulsion against globalism and elitism.

Schlafly entered the national stage when she self-published “A Choice Not an Echo,” a 120-page polemic proclaiming Barry Goldwater as the voice of true conservatism against the Northeastern liberal establishment. When Schlafly endorsed Trump a half-century later, many conservatives, including some of her most ardent admirers and family members, wondered about the seemingly abrupt shift from Mr. Conservative to Trump, a man of changing and at times undiscernible ideology.

Yet the disconnect was not as jarring as it first appeared. The signal consistency in Schlafly’s political outlook was her profound opposition to the Republican Party establishment and globalism. She represented a grass-roots populist sentiment that distrusted party elites, internationalism and crony capitalism. Schlafly tapped into this sentiment in “A Choice Not an Echo” and her fight against the ERA, and she proved remarkably adept in balancing dual allegiances to the Republican Party and a grass-roots base tempted by third-party candidates.

“A Choice Not an Echo” articulated Schlafly’s case against the “kingmakers,” composed of financial interests who sought a “convergence” between the parties. Schlafly argued that this group had manipulated the party into nominating candidates who were not true Republicans: Alf Landon in 1936; Wendell Willkie in 1940, Thomas Dewey in 1944 and 1948. She shied away from accusing the popular Dwight D. Eisenhower of being a kingmaker candidate, but it didn’t take much reading between the lines when she argued that the 1952 nomination had been stolen from conservative Sen. Robert Taft of Ohio.

Schlafly’s argument reflected both purist ideology and factional Republican politics. She voiced the ideology of the Old Right, leery of international involvement, anti-Soviet and insistent on U.S. military superiority. At the same time, the Goldwater movement represented the takeover of the GOP by Sun Belt and Midwestern activists.

This parsing of ideology and real politics played out strangely at times. For example, in 1968, Schlafly threw her full support behind Richard Nixon over Ronald Reagan, who had been elected governor of California two years earlier, because she considered Reagan inexperienced on foreign policy and soft on nuclear strategic policy.

In opposing the ERA a decade later, Schlafly took on the establishment within the Democratic and Republican parties, as well as Hollywood, the media and the feminist movement. Her success came because she united various factions on the right to come together under a single slogan, “STOP ERA,” which encompassed various points of opposition. Her campaign tapped into evangelical Christians, a lesson for party strategists, who began organizing evangelical voters in the 1978 midterm elections. The emergence of the religious right allowed Republicans to win the White House five out of seven times from 1980 to 2004.

Schlafly had found herself disappointed by Nixon, and in 1980 she threw her support to Reagan, who had become a hero of the Republican right. Although she was denied an official position in the administration, her support of Reagan remained unqualified, unlike some other grass-roots conservatives, who complained of tax hikes and a failure to dismantle the welfare-regulatory state.

For the next 20-plus years following the Reagan presidency, Schlafly searched in vain for a candidate who represented another “choice not an echo.” She refused to endorse George H.W. Bush, George W. Bush and John McCain in their attempts for the White House. She did back Mitt Romney in 2012, largely in reaction to Obama.

But Schlafly’s true candidate came in 2016 with Donald Trump. In her eyes, he represented all she had been looking for after Goldwater and Reagan. Here was a nationalist, a trade protectionist, immigrant restrictionist and a neo-isolationist. She dismissed arguments that Trump was not a true conservative, a candidate ignorant of constitutional principles, religious values or family values, to come out in full-throated support of Trump. Whatever inconsistencies in Trump’s agenda — his favorable comments on Vladimir Putin, for example — Schlafly managed to overlook.

In her final days, Schlafly fought what she considered the good fight, endorsing Trump and helping him win the party’s nomination. Her unqualified and emotional support of Trump troubled many of her followers and family members, but she witnessed at last what she had worked toward for seven decades: the triumph of the populist right against the party establishment.