A voter casts his ballot during the 2012 U.S. presidential election at a polling station in Staten Island. (Keith Bedford/Reuters)

William R. Sweeney Jr. is president and chief executive of the International Foundation for Electoral Systems. Chad Vickery is director of IFES’s Center for Applied Research and Learning, and Katherine Ellena is the organization’s senior legal specialist.

Is the U.S. presidential election vulnerable to manipulation by a losing candidate? Could the integrity of our electoral process be successfully challenged? Unfortunately, the answer to these questions is yes.

The International Foundation for Electoral Systems (IFES) has supported the integrity of political and electoral processes in more than 145 countries for nearly 30 years. We have developed a rigorous methodology to analyze vulnerabilities throughout the electoral process, drawing on international standards and commitments that stem from fundamental rights guaranteed in the Universal Declaration of Human Rights, International Covenant on Civil and Political Rights, and other international accords. We have applied this in multiple countries to fortify elections against malpractice, fraud and systemic manipulation.

From this global perspective and experience, we have increasingly seen the credibility of elections — and, in some cases, the stability of the election environment — hinge on the ability of electoral institutions, and in particular the election dispute resolution process, to withstand increasingly sophisticated political manipulation.

In multiple countries, we have witnessed the emergence of a campaign strategy whereby candidates, often supported behind the scenes by international communications strategists, cast doubt on the integrity of the electoral process and the institutions that manage it during the pre-election period, initiate post-election litigation challenging the results and take advantage of vulnerabilities in the process to derail or establish lasting doubts about the legitimacy of the outcome.

This challenge to electoral integrity is particularly acute in developing democracies, where legal frameworks are often ambiguous, processes may be less resilient to manipulation and a climate of insecurity, impunity and unaccountability may exist.

In 2014, ahead of the presidential election in Afghanistan, candidate Abdullah Abdullah and his supporters began to express fears of “industrial-scale” fraud, vote-rigging and manipulation of the electoral process. After the election, Abdullah boycotted the formal complaints adjudication process, claimed victory and threatened to establish a parallel government, while his supporters threatened unrest. The final outcome involved a brokered political agreement that departed from most standards for a credible election and complaints adjudication process, and official results from a nationwide electoral audit were never released.

Weeks after the Afghanistan election, almost 4,000 miles away, Indonesian presidential candidate Prabowo Subianto claimed “massive, structural and systematic” fraud in the election process, before ultimately withdrawing from the counting process, claiming victory based on allegedly falsified exit polls and filing a case in the country’s Constitutional Court, contesting official results. After weeks of televised hearings, the court’s nine judges produced a detailed written statement noting the absence of any credible evidence of widespread fraud and unanimously rejected the case, handing victory to Joko Widodo.

The similarities in these political strategies were stark, but the difference in outcome even more so. The level of vulnerability in the process or institutions responsible for the resolution of election disputes can have a profound impact on whether results can be accepted.

Developed democracies such as the United States are not immune to this threat to electoral integrity, and the 2016 U.S. presidential election process is facing key vulnerabilities that may represent a new and concerning test of the resilience of our constitutional democracy.

Looking at the electoral dispute resolution system, the U.S. legal system is in a uniquely vulnerable position due to the current 4-4 liberal-conservative split on the Supreme Court. If a candidate refuses to accept the election results for whatever reason, including claims of “rigging,” he or she will need to file cases in each state in which the results are contested. Given recent discourse on aging voting technology, voter-identification challenges and the vulnerability of mail-in ballots, this kind of litigation seems inevitable.

Such cases would ultimately end up at each state’s highest court, whose holding could be appealed to the Supreme Court. This was the path Bush v. Gore took in 2000.

Unlike in that year, however, it is possible that there would be no majority on the Supreme Court capable of settling the question. If the court voted along ideological lines, we would have a 4-4 split, and the state-level decision would hold. If that had been the case in 2000, the state Supreme Court in Florida would have decided the trajectory of the election, not the U.S. Supreme Court.

This could lead to contradictory decisions among states, drawn-out recounts and entrenched legal battles. Delays caused by these state-level legal challenges could also cause states to fail to resolve post-election disputes within the deadlines provided by federal law, which would transfer any final decision on state results to Congress.

If there are lingering disputes, the 12th Amendment to the Constitution could even come into play. In that event, the newly elected House of Representatives could wind up choosing the president from among the top three vote-getters.

Is this a likely outcome? Probably not. However, IFES has examined election integrity vulnerabilities around the world over many years, and the vulnerability in the U.S. election-dispute resolution system is real. The race so far has also been characterized by surprises. We have seen sophisticated political manipulation work in other countries, and recent complaints from one presidential candidate about the credibility of the electoral process and the likelihood that the elections will be “rigged” certainly make one wonder whether this type of sophisticated political manipulation is being tried in our system.