A build focusing on powerful hand to hand combat, tanking damage and nanomachines, son.
Your primary weapons in both hands should be the caestus, due to its high strength scaling, fast attacks, and the fact that Senator Armstrong also uses his fists. Your right hand one should be prioritised for upgrading as you will likely find yourself stun locking most enemies with the two handed heavy attack which only uses the right caestus. You should also try to obtain at least one firedrake stone which should be infused into your right caestus for fire punches like Armstrong's.
You should also have 2 spell casting items, a pyromancy flame in your right hand and a miracle chime in your left.
You're not one of those beltway pansies, so just like the great Senator himself, you will be wearing only your pants, the falconer pants to be precise as from the back they resemble trousers, because you don't need armour.
If your can, enter the covenant of champions and collect 50 awestones to obtain the vanquisher's seal, which gives your regular punches very strong attacks with good strength scaling, besides, Senator Armstrong does use his fists, not a caestus right?
You should have 4 spells in this build, 2 of which are pyromancies, Iron Flesh, giving you damage resistance representing your nanomachines (son) and Chaos Storm as this resembles a move Armstrong can use.
The other two are miracles, these are heal as Armstrong can do this too, and force, as we see armstrong being able to knock a pile of rubble off of him effortlessly with a shock wave, but never using it in battle indicates it does no damage so it is closer to force than anything else.
You should strive to level up your strength first, as the ability to stun lock enemies with your two handed heavy attack and kill them coupled with high strength will allow you to dispatch your foes with ease. High strength is also useful against enemies such as bosses that you can't stun lock as you can kill these much faster. As you willegando be levelling strength first it is recommended, but not at all required, to pick knight as a starting class, as the high starting vigor allows you a fair amount of damage right from the start of the game.
What order you level up in after that is entirely up to you, and by no means do you have to follow this exactly, I only picked 20 endurance as this is when it starts increasing by 1 stamina instead of 2 but you can go higher, likewise if you want you could choose more, less or just a different set of spells if you feel they also match Armstrong's move set.
When designing your Senator Armstrong, the receding hair looks the best.
When fighting enemies, do not forgot to repeatedly make Armstrong quotes such as:
"I'm gonna knock you out!"
"The greatest nation demands your blood!"
"Feel the wrath of the U.S.A!"
"America needs you to die, Jack!"
"Don't fuck with this senator!"
"Man to man, I can't be beat!"
"This is the greatest fight, of my life!"
"You know what? Fuck this war. I just want you dead!"
After taking a staggering or big hit - "Heh heh heh, THAT one hurt!" or "Okay, now I'm mad!"
Upon taking a small hit while Iron Flesh is active - "Nanomachines, son. They harden in response to physical trauma!"
Upon taking a fairly large hit, but not large enough to turn the tides of battle - "Alright, I'll give you that one." or "Most impressive, Jack. Most impressive."
When fighting smaller enemies - "Crush you like a god damn bug!"
When using pyromancy - "Ashes to Ashes, motherfucker!"
Upon landing a big hit or final blow - "Die you piece of shit!"