“I could never lend myself to any transaction, however respectable, that would commercialize on the prestige and dignity of the Presidency” said Harry Truman, the 33rd US President, after leaving the White House. Despite returning to modest financial circumstances post-presidency, he refused to lobby, accept consulting fees or work as a business executive.

Today’s political leaders in America and in Britain do not share Truman’s reservations when it comes to cashing in after leaving public office. In fact, their brazenness gives the appearance of impropriety, which has contributed to the mistrust of governments that underpins today’s populism. If we are to restore trust, we need to better regulate their income-earning activities.

Former US President Barack Obama earns $400,000 per speech from Wall Street firms (some of which he donates to charity) while ex-PM David Cameron is reportedly paid up to £120,000 for similar speeches. George Osborne, his former Chancellor, also gives high-paid speeches, while earning £650,000 per year for working one day a week at BlackRock, an investment firm.

These ex-politicians are not unique. In both countries, over the last few decades, former government heads and cabinet members have made fortunes through consultancies, corporate board memberships and speeches to business organisations. Although this trend started earlier in America, such wealth accumulation was legitimised by the pro-free market ideology embraced by Margaret Thatcher and Ronald Reagan in the 1980s. This ideology inherently undervalued government service. High public office, once the culmination of a career, evolved into a stepping stone to riches.

In the United States, former presidents are partly motivated by their drive to mobilise funds for their presidential libraries, which have become sinecures from which to shore up their legacies.

To critics, such pursuit of wealth gives credence to allegations of a cosy relationship between government and big business, often described as "crony capitalism". Small wonder that Hillary Clinton’s paid speeches to the investment bank Goldman Sachs, after her tenure as Secretary of State, became an issue during the US Democratic Party primaries in 2016.

Even if leaders are immune to the influence of money, perception matters. If citizens believe leaders modified their behaviour in office in anticipation of later rewards, their suspicion towards government is likely to increase. It is this mistrust that led some to vote for Brexit in Britain and for Donald Trump in the United States.

As we cannot count on today's former leaders to possess Harry Truman’s restraint, we need to rely on rules to curb their behaviour. In the UK, the government does have rules, which the Advisory Committee on Business Appointments (ACOBA), a governmental body, uses to advise former PMs and senior government officials within two years of them leaving office. However, in a report, earlier this year, the parliamentary Public Administration and Constitutional Affairs Committee described ACOBA as “toothless”. It said that “The regulatory system for scrutinising the post public employment of former Ministers and civil servants is ineffectual and does not inspire public confidence or respect.”

In America, Congress enacted a criminal statute that includes conflict of interest laws for former government officials. However, former presidents are glaringly exempt from these laws. In both countries, the restrictions tend to narrowly focus on lobbying and longer term employment opportunities. They are not tailored to address speaking fees for specific events. Above all, the restrictions do not adequately consider the larger issue of public perception. All this needs to change.

Enhancing and enforcing the rules will be a step in the right direction. This will likely discourage those from political leadership who see high public office as a stepping stone. However, it will not deter those sharing Harry Truman’s reverence for such office – they are also the best hope we have for combatting the broader influence of money in politics.

Arslan Malik teaches at the Schar School of Policy and Government at George Mason University, outside Washington, D.C. Until earlier this year, he worked at the U.S. Department of State.