A former top aide to Sen. Bernie Sanders' (I., Vt.) faltered in his bid for a U.S. House of Representatives seat on Tuesday, despite receiving extensive political backing from the self-described Democratic socialist.

Pete D’Alessandro, who was instrumental in helping Sanders wage a credible challenge to former Secretary of State Hillary Clinton during the 2016 Democratic presidential nomination, finished third in the contest for the Democratic nomination in Iowa's 3rd Congressional District, according to the Des Moines Register.

From 2015-2016, D’Alessandro served as Sanders' campaign coordinator in Iowa. His efforts on behalf of the senator resulted in a nail-biting race between Sanders and Clinton in the 2016 Iowa Caucuses, with the former secretary of state winning the state by the closest margin in the contest's history.

When announcing his run in April 2017, D’Alessandro initially looked as though he would be able to build off Sanders strong support in the Hawkeye state. The candidate ran a progressive style insurgency campaign, similar in mold to Sanders' 2016 effort, by emphasizing his support for the senator's hallmark policy agenda. D'Alessandro ran on his support for a $15-an-hour minimum wage, tuition-free college, and Medicare-for-all.

D’Alessandro, however, failed to repeat Sanders' initial success at the ballot box. On Tuesday, he garnered only 15.6 percent–8,595 votes–of the total 55,247 vote primary electorate. The candidate's vote total placed him firmly in third place behind the race's front-runner, Cindy Axne.

The poor showing was compounded by the considerable political capital Sanders expensed in support of D’Alessandro's bid. The senator journeyed to Iowa in February to host a rally on D’Alessandro's behalf and utilized his sweeping donor network to solicit money for the candidate. In May, when polling showed D’Alessandro falling behind his two primary competitors, Sanders stepped in to bolster the fledgling campaign by recording his only tv ad of the 2018 election cycle.

The Vermont senator wasn't alone in his efforts. Our Revolution, the political advocacy group that spun-off from Sander's 2016 campaign, endorsed D’Alessandro early in the primary process and attempted to underwrite his candidacy through building grassroots support.

Axne, a small business owner and prior Iowa Democratic official, is set to face incumbent Republican Rep. David Young in the general election this November. Young has represented the 3rd Congressional District, which encompasses Des Moines and its southwest suburbs, since 2014. Although the district is marginally Republican on paper, President Donald Trump carried it over Clinton by a close margin of 4 percentage points in 2016. Young, in comparison, was overwhelmingly re-elected the same year by 14 points.