Our British democracy is a presidential system There are specific and substantial reasons for this in each case. The various Prime Ministers had immense flaws and were leading in an unavoidably complex context. In the case of Cameron he swims against the historic tide, half knows this is the case and sometimes seeks to move with the waves, only to be drawn rightwards by instinct and his party. This is the fundamental reason why he is the latest Prime Minister to be in intense trouble. But he is a talented politician and an intelligent student of politics. His tutor at Oxford, Vernon Bogdanor, although no fan of Cameron's policies, still regards the Prime Minister as too easily underestimated. Listeners of this morning's Today programme were reminded that Cameron is a goodish interviewee, not in Blair's league as a communicator, but calm, good-humoured and delivering answers with at least an appearance of clarity. Indeed, his public intervention yesterday had a familiar ring. In the Blair era, a frenzy would erupt about something or other, there would be days of speculation over Blair's fate, he would then give a calm interview or hold his monthly press conference, and the journalists would declare that he was in command and authoritative. There would be a pause until the next crisis. Again, I stress that in Cameron's case there is good cause for the headlines of recent days. Politics is always extraordinary, but it is going through one of its more tumultuous sequences, with a peacetime coalition, the rise of Ukip, a referendum in Scotland and a daunting economic crisis. As a Prime Minister, Cameron must keep Nick Clegg on board (relatively easy on most issues except the big one of Europe), address the concerns of his party (not easy), and keep more than one eye on Ukip (nightmarish). He is doomed to eternal fragility and to perform contortions that would test the most lissom gymnast. The modern media heightens the sense of crisis for Prime Ministers. While listening to Cameron on Today, I kept an eye on Twitter at the same time. You can bet his senior aides would have been doing the same. Within seconds of leaving the studio ,Cameron would have known the verdict of a thousand commentators. He probably checked himself. A few years ago, a Prime Minister rarely appeared on Today and if he or she did the verdicts would arrive in the following day's newspapers, by which time most people will have forgotten the original interview. Now the political temperature is at boiling point around the clock. The media culture both reflects and fuels our presidential culture. While Prime Ministers define and shape our politics, most other politicians are unknown. This focus on a single individual makes the demands on modern Prime Ministers almost impossible. They must seem presidential at all times, wholly in command, even though they lead parties that are powerful and on which they depend for support. As a near President, the Prime Minister must be in control of every domestic policy. The Prime Minister is also the main voice in foreign affairs. At all times, he or she is leader of a party and an army of MPs. In addition, Prime Ministers must convey messages through the never-ending media or respond to various frenzies. Consider the madness of Cameron's past few days in Washington for talks with President Obama while seeking to deal with an insurrection over Europe that he described yesterday as "disagreeing over something we agree with." Meanwhile, he had to address the eruption of "loongate" in which a member of his entourage was accused of being disparaging to activists, while deciding on the parliamentary tactics to see off his rebels in the gay-marriage vote. Cameron has many faults but the accusation often made against him, that he is lazy, is comically misplaced. Goodness knows what else was going on behind the scenes, but you can be guaranteed that Cameron would be taking many other decisions. Blair once told me that each day he faced decisions that came down to the following question: Should I cut my throat or slit my wrist? Any wrong call in government and the Prime Minister must answer. Not surprisingly, they get burnt out, make mistakes, despair, go mad. I am told that Cameron has wondered aloud to friends at times whether it is worth carrying on, before deciding unsurprisingly that it is. He looks much fresher than some of his predecessors did. For all the specific reasons that explain the destabilising crises that unnerve Prime Ministers, there is one constant factor. No 10 is under-powered. This townhouse, with its tiny units of advisers and officials, cannot cope with the modern demands of leadership. When the then Prime Minister of France Lionel Jospin visited London, he was introduced to Blair's economic adviser. Jospin asked Blair where the rest of the adviser's department was. He was told that he had only one economic adviser. Jospin thought he was joking. There needs to be a big, well-resourced highly political Prime Ministerial department to reflect the responsibilities of a modern Prime Minister. Precisely because of all the weekly crises, Prime Ministers quickly become too weak to establish a proper department, fearful they will look too arrogant. The move can be made only at the beginning, when Prime Ministerial popularity is fleetingly high. The next Prime Minister should announce his plans to appoint political advisers, top officials, and party-based people in a big new department on Day One - before the crises erupt.