Swing voter decides who Marines will salute

The film: Swing Vote (2008), directed by Joshua Michael Stern. Not to be confused with the 1999 TV movie of the same name.
What happened: Molly (Madeline Carroll), the daughter of drunk Bud Johnson (Kevin Costner), attempts to vote in her father's name at the polling place in Texico, New Mexico (which happens to be a real place, close to the intersection of I-27 and I-40), unwittingly giving him the tie-breaking vote that will determine the outcome of the 2008 presidential election. The incumbent, Andrew Boone (Kelsey Grammer, as a smarter version of George W. Bush), has one of those walk-and-talk meetings with advisors in the corridors of the White House early on in the film. In one hallway, two Marine Corporals (both in their second enlistment) stand guard, wearing dress blue uniforms complete with the white hat. As President Boone passes by, the Marines salute and Boone returns the salute.
Why it's wrong: Despite its Army-like rank insignia, the Marine Corps is a naval service. Marines in uniform wear their hats (covers) when a) outdoors, and/or b) carrying a weapon. Marines in uniform salute only when wearing a cover, otherwise they stand at attention. This is ingrained early on in boot camp: a Marine walking around outdoors in uniform but no cover would be more embarrassed than if he was naked. Likewise for a Marine indoors wearing uniform with cover but carrying no weapon.
So the two Marine guards inside the White House, as far as I can tell, don't carry weapons, so they should not be wearing their covers. Come to think of it, why are there Marines inside the White House, guarding some random hallway? Wouldn't they be outside, guarding the entrance? And even if there are Marines inside the White House, the Secret Service would probably not let them have weapons. Remember in real life how nervous George W. Bush gets around Marines with unloaded rifles (as in Marine Boltgate 2005). Granted, Boone is a much different man from Bush: more articulate, and better educated than Bud Johnson, too. Perhaps Boone wouldn't be afraid of the Marines.
And another thing: I'm somewhat skeptical that a Corporal assigned to the White House would be in his second enlistment. A Marine good enough for a White House assignment would probably be good enough to be a Sergeant by the time he/she earns his/her first service hashmark (the one yellow stripe close to the cuffs in the dress blue uniform jacket, not part of the rank insignia, which is closer to the shoulder). In news footage I've seen Lance Corporals and Corporals at the White House. The Lance Corporal should certainly be in his first enlistment, or else he's done something to get demoted and is probably not worthy of serving at the White House. For a Corporal, this is somewhat borderline, so I suppose one second-enlistment Corporal at the White House is within the realm of possibility. Yet in Boone's White House you have not one but two Corporals in their second enlistment.
Spoiler alert: I'm not going to nitpick the plausibility of the film's basic premise. With almost two million people in New Mexico, it would be rather surreal for any election to come down to one man's vote. But then again, the 2000 presidential election being decided by the Supreme Court was quite surreal, too.
But I think this film wimps out at the end. Bud Johnson goes in to cast his tiebreaking vote, to decide between incumbent Boone and his Democratic opponent, the appropriately named Donald Greenleaf (Dennis Hopper). Presumably, his votes for the lower offices won't matter. After Bud closes the privacy curtain, the end credits roll. His vote remains a dangling thread at the end of the film. Doesn't that weaken the message that voting matters? On the other hand, the film could have been accused of partisanship if the Bud's vote had been shown. It's a no-win situation for writers to put themselves in, I suppose.