With Checks and balances and powerful individual Congressman it's virtually impossible to get a big program through. There're almost a dozen veto points (ie: the sub-committee, the full committee, the full house, all three processes in the Senate, the reconciliation committee to get the bills to say the same thing, vote in both the house and the senate on the bill; then the President has to sign). You either need a) a vast consensus that something is a good idea, b) a small idea that threatens nobody, or c) a major push by somebody with clout. NASA's too-small budget is $18.4 Billion a year, which is $184 Billion in the 10-year-budget window; and thus can't be too small to pay attention to. The 'consensus' that exists today is low tax, low spending, free-market and a government space agency does not fit the plan. And nobody is gonna push NASA when something immediate is always sucking up the oxygen in the room.
Thus we have a system that has no trouble passing a new tax break, but can't for the life of it agree on funding the Border Patrol because everyone is in a death struggle over Obama's immigration plans.
OTOH, let's say we had the Canadian Constitution. If Obama was Prime Minister he'd necessarily have a majority of the lower house, and he'd also have veto-power over everyone on his side's re-election (you can't run for a seat in Canada without the signature of the Party leader on your papers, altho this year all the parties swear they won't veto any of their local riding association's nominees). He'd also have control of the Senate because the PM appoints Senators. Reconciliation would consist of him saying "hey Senator, that was a good point, we'll go with your bill" and a rubber-stamp. The bill would be signed by a Governor-General Obama appointed.
Don't get me wrong, there are checks on a PM's power. Notably he has to have approval from his Cabinet, and his Parliamentary majority to keep his job, and if he loses either he tends not to be PM for very long (Chretian was forced out by his Parliamentary caucus), but while he retains the confidence of Parliament a Prime Minister can just do shit. He doesn't have to worry about whether the other party will put his proposal in Subcommittee A (whose Chair hates him and won't even schedule a vote on principle) or Subcommittee B (whose chair hates him, but loves the idea and will vote on it after only three hours of Obama-bashing). PM Obama fires both Subcommittee Chairs and if Parliament doesn't like it there's a new election and within four months the people will have picked a Palrliament where the PM and the Subcommittee Chairs are on the same side.