* The US Constitution says that US Presidents can be overruled by the US Congress – so even if he does become President, his powers will be limited;
* He's currently [in 2008] very popular abroad, but is less popular amongst Americans – and it will be American voters who'll decide whether they want him as US President, not foreign voters;
* He may not even win the election – and if he loses, he'll obviously have no powers to change or do anything.

So it's saying that, even if he does become President, there are lots of basic constitutional laws in America, such as those describing the relationship between the President and Congress, that he won't be able to change.

The article simply says, no matter how different is Obama, he has to follow certain requirements and rituals set by the Washington establishment. In other words, he can not act freely as he wishes.

"even if he does become President, there are lots of basic constitutional laws in America, such as those describing the relationship between the President and Congress, that he won't be able to change."

Mr Obama has not repealed the basic laws of politics - just means Obamas come and go, but the basic laws of politics ( political etiquette, if you wish) last I checked, are still there. In Russian they say "пока еще никто не отменял"

Эту мысль, кстати, автор и сам раскрывает далее, причем буквально в следующей же фразе:

Most obviously, he may not win. … Mr Obama still definitely has the edge, but opinion at home diverges sharply from that in most of the rest of the world.

И далее продолжает раскрывать:

Second, President Obama would not be answerable to the world that so adores him. A president is elected by America's more ambivalent people, and is accountable only to them. …

Finally, there are some disquieting signs of a tendency on Mr Obama's part to tailor his message to whichever audience he is talking to. … [and his] two-steps have become Astaire-like.

То есть не обольщайтесь: он говорит красивые европейские вещи, возможно, отчасти, потому что он говорит их европейцам. А делать он будет то, что нужно чтобы получить поддержку американцев, своих избирателей, а не европейцев, какими бы близкими по духу они ему ни были. Таковы суровые законы политической физики, и отменить их не получится даже у самого совершенного оратора.

И избиратель или истеблишмент – это важно. Избиратель – это базовое. А истеблишмент с его условностями (игра по определению условность) не базовое, можно играть с ним, а можно и против него.

За примерами далеко ходить не надо – ваш нынешний президент в праймериз весь истеблишмент своей партии послал лесом. Они все пытались ему втолковать, что ты, мол, со своим безвкусным нарциссизмом иди домой дальше строить гигантские фаллические символы и писать на них свою фамилию, а в дело тонкое, в политику, не лезь, здесь думать надо. Он послал их и они дружно все со своими установившимися правилами пошли. А потом и побежали. За ним. Как только поняли, что избирателю как раз его вот этот безвкусный нарциссизм и все такое и нравится.

Правда, ему потом удалось послать и избирателя, на самих выборах, и выиграть, набрав заметно меньше голосов, чем соперник, но это уже случайность, уж больно хорошо для него они легли, голоса, и вряд ли можно быть настолько тонким электоральным тактиком, чтобы такой расклад просчитать и создать специально. Это уже сработал не базовый закон политики, а ее атавизм.

The sort of 'laws' you're talking about, examples of which you show in your link are, of course, more philosophical laws than real, legal laws. They're 'laws' which describe how politicians and people tend to think and behave. That was also what I thought the author meant by 'laws' when I first read the asker's sentence: that the author was referring to philosophical laws rather than real, statutory ones. (The first example I thought of was Lord Acton(?)'s quotation "Power corrupts, and absolute power corrupts absolutely", although your list is much more comprehensive).

Then, because the asker had given very little context, I decided to search for the original article. It's at http://www.economist.com/taxonomy/term/108?page=373 . The asker's quotation is about ⅓ of the way down. If you read the whole paragraph and the ones above and below it, you'll see that in fact the author's talking not about general, philosophical laws (which I also assumed at first), but about real, constitutional (statutory) US laws. The three examples I gave at 23:57 are in fact all taken from the article, and 00002 has listed a few more. The 'laws' the author refers to are all ones which form part of the US Constitution and lay down: the relationship between the Congress and President; who can elect the President and who can't (Americans, not foreigners); how elections must be conducted; and, as the author makes clear, how you can't have any presidential powers at all, unless voters firstly elect you President.

So the author's not talking about general, philosophical 'laws' of human behaviour at all; he's talking about real, US constitutional/legal laws which, he also makes clear, Obama has no powers to change.

Secondly, in my understanding of the author's points, he says that foreigners should hold their horses. Why? Because there are things (the basic laws of politics) that nobody can change, even a "marvellous orator" like Obama. And those things are:
1. He needs to be elected at the first place, and that's up to Americans.
2. Congress need to be on his side.
3. Sometimes he looks like a liar and can't be trusted. (but that's OK for a politician)

Do you really think here, that the author is talking about changing US legal system? Or it is about political realities in connection with presidential election?

He's saying that Obama's supporters abroad should be cautious if they expect him to win and then be a good President, and begins by giving the three reasons you've listed. The first two of these are linked to real (US statutory/constitutional) laws governing how a US President gets elected, who can and cannot vote for him, and his relationship with the Congress if he is elected. When the author says Obama "has not repealed the basic laws of politics", he's not implying that he's already been President but failed to repeal them; he's simply saying that, however good Obama may be as an orator and tactician, those statutory/constitutional laws are still the same as they've always been, and so he'll have to operate within them.

The third reason the author gives isn't a rule or law; it's simply an observation, as you say, that Obama says different things to different audiences, and so when he promises to do things, you can't trust him to do it if he does become President. (Yes, typical of most politicians!)

You say "there is nothing in the article pointing [to] any legal law". No, it doesn't say "legal law" specifically, but it's obvious that that's what he's talking about, because the rules covering how US presidential elections are conducted, who can and cannot vote, and a President's relationship with the Congress, will all be written into US statutory laws, probably the US Constitution. Where else would they be??? My point was simply that 'repeal' here doesn't refer to philosophical 'laws' such as those listed in your link; it refers to real (statutory) laws.