Helen, the two-party system wasn't legislated, it simply evolved. Third parties occasionally run candidates but usually lose. There were four parties/candidates running for president in 1860. Lincoln won, but almost two-thirds of voters voted against him. For many practical reasons, third party presidential candidates rarely generate much interest, though they can certainly influence the outcome of an election by drawing off voters from one (or both) of the others, sometimes predictably - which makes them dangerous if cynically financed by mega-donors to one of the other parties.

It would be nice if the federal government gave each candidate an equal sum of money to run on, while forbidding any other funds to be used. But Congress would never approve such a plan, because each party thinks it will gain a decisive edge by raising more money.

The 2010 Supreme Court decision "Citizens United v. FEC" now allows corporations and "political action committees" to donate unlimited funds to the candidates of their choice. Their reasoning was that campaign contributions are a form of free speech. The result, of course, is that mega-donors now influence the parties and candidates as never before, often giving huge amounts to both sides, so that no matter who wins, they'll still have plenty of influence. Nor must the parties reveal the specific sources of many such contributions.

Power in the U.S. isn't invested in one person (yet), though it's easy to think so, since the president gets credit and blame for everything that happens.

As for the electoral college, its flaws are becoming ever more obvious. I doubt much will be done about it in the so-called "foreseeable" future, however.

Compulsory voting doesn't appeal to me. It makes every fool who doesn't care and who would prefer to stay home is made cast a vote almost at random. There are enough fools voting already.