One of the worst kept election secrets in recent history was finally revealed yesterday. Hillary Clinton announced she was running a second time for the presidency of the United States. After failing to land the nomination back in 2008, Clinton’s run to front the Democratic tickets in 2016 looks a much more straight-forward process (in theory).

The next US presidential election, however, is still 574 days away, whilst our general election is in just 23 days. Yet this week is ‘manifesto week’, and although we have just over three weeks until the polls open, Clinton made her announcement about running for President before the major political parties unveiled their own manifestos.

This seems somewhat bizarre, but in fact it speaks to the broader point of the different election systems in the US and the UK; presidential vs parliamentary. One of the hallmarks of the US presidential system, that it has fixed terms, is arguably the most significant constitutional change adopted by the Coalition Government here in the UK.

David Cameron’s recent declaration that he would not stand for a third term as prime minister was partly a result of this change. The Fixed Term Parliament Act means that after 7 May, there will not be another election until 2020, barring any fall of the government.

Speaking to Newsnight following Cameron’s announcement, Chief Whip Michael Gove compared Cameron’s decision to that of an American President only serving two terms. Although the systems may have moved closer together with the adoption of fixed terms, there is still a key distinction between a second term president and a second term prime minister. The president is not dependent on the legislature for support and constitutionally cannot be removed, barring any reasons for impeachment.

A president coming to the end of their second term is often labelled a ‘lame duck’, unable to pass legislation as the legislature prepares for the upcoming battle for Congress and the White House. President Obama has recently demonstrated one upside to the second term president, though, with his notable successes in the area of foreign policy.

With greater freedom over the direction of US foreign policy, Obama has managed to secure a nuclear deal with Iran which, for whatever its detractors say, is a better option than anything else on table. His meeting over the weekend with President Raúl Castro of Cuba ends over 50 years of US isolationism with the country, and is another welcome move.

The Fixed Term Parliament Act would offer Cameron no such joy. In fact, following a potential EU referendum in 2017, the Conservative Party will be faced with the prospect of re-uniting after a campaign which will see some party members on the opposite side of the In/Out debate. There is a widely-held belief that Cameron may use this moment to bow out.

This is where Hillary comes in. Clinton may enjoy nationwide appeal in the United States, but presidential candidates still need time to lay out their vision to the nation, to build up support, finance and personal brand. This is why Clinton, along with a couple of candidates for the Republican Party have started the campaign process now.

It’s almost impossible to imagine a scenario where any prime minister, Cameron included, would serve right up to election day for another party member to take over the following day. It would be a confusing signal to the electorate as to who is in charge. Plus the next leader would no doubt already be a member of the cabinet and wedded to the position of the current prime minister. Whoever is to lead the party in 2020 needs time to assert their leadership in the run up to that election.

Cameron may have given an “honest answer” to an “honest question” about his future plans, but his intention is ultimately at loggerheads with the constitutional mechanics of the situation. Still, when Americans eventually do go to the polls in 2016, they can at least be assured of the fact that either the Democrats or the Republicans will control Congress, the White House, or both. On 8 May we may not be so lucky.