President Trump is almost certain to lose a valuable ally in Argentina as conservative Mauricio Macri is likely to lose the upcoming presidential election this Sunday to a left-wing rival backed by a running mate who still looms large over the Latin American country.

On the ticket with Macri rival Alberto Fernandez is former President Cristina Fernandez de Kirchner, who was president from 2007 to 2015. The frontrunner is considered a moderate Peronist, the movement named after Argentina’s left-wing working-class populist Juan Perón, who first came to power in 1946.

His running mate, Kirchner, is a more radical leftist that commands a strong and loyal following. The Fernandez/Kirchner ticket currently leads Macri 54%-31.%, according to the American Society/Council of the Americas.

During Kirchner’s rule, relations with the U.S. were tense and Washington had very little confidence in Argentina. The election of Macri in 2015 signaled the possibility of better relations and a friendlier investment environment.

But according to polling, the Fernandez/Kirchner ticket looks set to beat Macri by approximately 52% to 34%

Macri is a moderate market-oriented conservative and developed a good relationship with President Trump, acting as a regional lynchpin in the Trump administration's pressure campaign to oust Venezuelan dictator Nicolas Maduro. His defeat could disrupt relations with the Latin American nation, especially if the new regime implements more confrontational economic policies or takes a more lenient position toward Venezuela.

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Argentina, which is host to an estimated 130,000 Venezuelan refugees, rallied behind President Trump’s campaign to isolate President Maduro and formally recognized opposition leader Juan Guaido as the legitimate leader of Venezuela. A Fernandez victory could radically alter Argentina’s posture toward Caracas.

Fernandez broke with the U.S. and regional partners on the stern position in opposition to the socialist ruler, saying that Maduro was “not a dictator.” Fernandez’s language is in stark contrast to the Trump administration’s maximalist policy and rhetoric toward Venezuela.

Fernandez’s domestic legitimacy will rely heavily on revamping the struggling economy. Inflation currently stands at 44 percent and economic growth has contracted 1.2 percent, according to the International Monetary Fund. The Argentine economy continued its decline even after the IMF offered Argentina a $57 million bailout in 2018, the largest loan package in IMF history.

If the economy continues its downward trajectory, it could weaken the new presidency and give rise to Kirchner.

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“If he falters, if the economy continues to stumble along, if his strategy becomes unworkable, then Kirchner will emerge as the stronger party. It is Cristina in the end that has the loyal following, and knows how to talk convincingly to ordinary Argentines,” Peter Hakim, Senior Fellow at the Inter-American Dialogue, told Fox News.

The question remains, however, if Kirchner will accept her role as a vice president with limited power, or if she will look to influence Fernandez’s decisions and lobby for her key allies to be placed in the government. A vulnerable president could provide space for Kirchner to maneuver herself as the main power-broker in Argentina.

“If the president and the vice-president fight for power after winning the election, there could be a serious battle at the very top of Argentina’s government, which could make the administration highly dysfunctional. This could make it hard for the new government to react to Argentina’s worsening economic situation,” Senior Analyst at Stratfor Adriano Bosoni, told Fox News.

Fernandez will likely attempt to co-opt members of the Peronist elite to consolidate his power, but Kirchner has a much more radical base of support.

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“Kirchner’s radical base of support includes marginal groups especially in the greater Buenos Aires, other governors, and her son’s youth movement “La Campora” which is a Bolshevik-like organization. When she was president she was closely allied with Chavez and Maduro,” Professor Emeritus at New York University, Juan Corradi told Fox News.

But she faces investigations into fraud and corruption, although currently enjoys immunity from arrest as a member of Congress, a status that would also apply as vice president.

Despite potential legal problems hanging over her, she remains immensely popular among Argentines who view her as a champion of the poor. Supporters wear T-shirts with her image and refer to her affectionately by her initials "CFK".

The political resurrection of Kirchner coupled with the dismal performance of the economy under Macri’s leadership is further depressing the business environment. Investors fear a return to Kirchner’s controversial economic policies under her previous term in office, with protectionist tariffs and greater intervention in the economy.

“The prospect of Cristina Fernandez and the Peronists back in the driver’s seat horrified the local business community and foreign investors, which has put additional downward pressure on the economy,” Hakim said.

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As Macri’s tenure in office appears to be drawing to a close, Washington should be prepared to lose a stalwart supporter of its regional foreign and economic policies.

The Associated Press contributed to this report.