If one wished to be uncharitable, one would suppose that a few Senators with powerful positions on committees overseeing NASA and with NASA contractors in their states were constraining the design space for NASA not for the good of the nation but to get themselves re-elected.
However, let's be charitable. Let's suppose the Senate rocket designers in fact have a 130 ton/ne payload in mind, a super-secret payload that has super-secret funding, because it sure isn't funded through NASA's
Let's suppose the SLS (Space Launch System or Senate Launch System, take your pick) gets built and the Senate gets to launch Super Secret Payload number 001. What? You mean that there has to be more than one payload to justify development of an entirely new rocket system?
Suppose that they get the rocket built and integrate the payload, and SLS could lift 130 tons to orbit but SSP001 is 130 tonnes. Oops! Meh, that sort of thing happens at NASA from time to time. Or suppose SSP001 is 129 tons, but once they get it up there they realize they need something twice as big. They can't do orbital rendezvous, which has hardly even been tried at all except in assembling Mir and ISS. So they'd need a rocket that could lift a 260 ton payload all at once. And eventually they'd need a rocket that could lift twice as much as that.
Well, why go for half measures? Why not just build the rocket we'll eventually need, right away?
What I propose is that NASA build a rocket capable of lifting 16 million tonnes to escape velocity. Surely that would be the biggest single payload that NASA would ever need. If we do that, then NASA will finally be able to get started with Beyond Earth Orbit manned exploration.
To be conservative, let's use 12 km/s as our delta vee and 300 s for our specific impulse. If we further assume that the mass of the ullage is negligible, the rocket equation gives us a total fully-fueled mass for our Somewhat Large Space Transport of around a billion tonnes.
Now that's a rocket!
Of course, a full flight test of such a rocket would be very expensive. And the logistics of mounting such a huge payload on top of the SLST would be difficult, thus employing lots of people in key congressional districts. There's also the minor inconvenience of there being no possible launch pad capable of supporting that mass without burning down, falling over, and then sinking into the swamp.
However, Gaia has smiled upon us, and what was once thought an environmental disaster of Biblical Plague proportions could literally be the launchpad to the future. Apparently (and I haven't been following this too closely, just what I see on CNN) the Gulf of Mexico is some sort of oil-slick covered watery desert of death due to some British guys or something. Well, liquid Oxygen and liquid Hydrogen are lighter than water, so you could just float the whole rocket out into the Gulf and you don't even need a launch tower. I totally stole that idea from Sea Dragon. Any launches of the SLST wouldn't harm any wildlife in the Gulf because that's all dead from corporate greed or something which was probably Bush's fault anyhow. My details on this are kind of hazy because I haven't been watching CNN much lately.
All the unemployed people in the Gulf States could then be put to work either by physically manhandling the 16 million tonne payload onto the SLST or by joining hands and singing Kumbaya. Either way, it's financial stimulus. It'll be a huge financial stimulus when that sucker gets launched, too.
note: The US Capitol building and its grounds cover about 16 city blocks, so about a 400 meter by 400 meter area. At 100 tonnes per square meter, that's 16 million tonnes.