Sergeant at Arms of the United States House of Representatives

[CTAtheist]

(a) Law enforcement authority
The Sergeant at Arms of the House of Representatives shall have the same law enforcement authority, including the authority to carry firearms, as a member of the Capitol Police. The law enforcement authority under the preceding sentence shall be subject to the requirement that the Sergeant at Arms have the qualifications specified in subsection (b).

https://www.law.cornell.edu/uscode/text/2/5605

Can Congress Jail Witnesses Who Refuse to Cooperate?
<snip>
But, just because there’s no physical jail doesn’t mean there’s no right for Congress to detain individuals — and in fact the Capitol Police do maintain a holding cell a few blocks away.

http://time.com/5023920/trump-russia-election-congress-capitol-jail/


Just sayin'

[tymorial]

1. The sergeant at arms already has a weapon. He/she has the mace

If a member becomes disruptive or "unruly" the sergeant at arms will be instructed to throttle the member with the mace until they submit.

Okay seriously, when a member is engaging in disruptive or unruly behavior the speaker can order the sergeant at arms to present the mace. This action is designed to restore order as it's a reminder of the rules of the house.

The last time it was threatened was in 1994. Carrie Meek was ordering Maxine Waters to leave the floor but Waters refused. There were suggestions from the house to present the mace and it appeared Meek was about to order that to occur when Waters stopped. It's only occurred a handful of times and not in the last 100 years.

[malaise]

2. This?

https://twitter.com/search?q=mnuchin+trump+tax+returns&ref_src=twsrc%5Egoogle%7Ctwcamp%5Eserp%7Ctwgr%5Esearch

[watoos]

3. Who will enforce it?

[malaise]

4. The Sergeant at Arms

[onenote]

5. The Sergeant at Arms has limited territorial jurisdiction

As the provision quoted by the OP indicates, the Sergeant at Arms has the same law enforcement authority as the Capitol Police. And the Capitol Police have very limited law enforcement authority. Specifically, the Capitol Police (and thus the Sergeant at Arms)
"shall have the power to enforce the provisions of this section, sections 1922, 1966, 1967, and 1969 of this title [1] (and regulations promulgated under section 1969 of this title), and chapter 51 of title 40, and to make arrests within the United States Capitol Buildings and Grounds for any violations of any law of the United States".

In other words, unless a witness wanders over to the Capitol Grounds, the Sergeant at Arms can't arrest that witness.

[CTAtheist]

10. I am not sure, there's conflicting info on the subject.

"From the Republic’s earliest days, Congress has had the right to hold recalcitrant witnesses in contempt — and even imprison them — all by itself. In 1795, shortly after the Constitution was ratified, the House ordered its sergeant at arms to arrest and detain two men accused of trying to bribe members of Congress. The House held a trial and convicted one of them.

In 1821, the Supreme Court upheld Congress’s right to hold people in contempt and imprison them. Without this power, the court ruled, Congress would “be exposed to every indignity and interruption, that rudeness, caprice, or even conspiracy, may mediate against it.” Later, in a 1927 case arising from the Teapot Dome scandal, the court upheld the Senate’s arrest of the brother of a former attorney general — carried out in Ohio by the deputy sergeant at arms — for ignoring a subpoena to testify.

The Congressional Research Service issued a report in July that confirmed Congress’s inherent contempt powers. It explained how they work: “The individual is brought before the House or Senate by the sergeant at arms, tried at the bar of the body, and can be imprisoned in the Capitol jail.” Congress can do this, the report concluded, to compel them to testify or to punish them for their refusal to do so.

https://www.nytimes.com/2007/12/04/opinion/04tue4.html

Plus, I have heard of a story (I googled, but could not find it) where a Speaker ordered the Sergeant at Arms to go into D.C. to someone's house, arrest someone, and drag them to the floor of the House.

[Pobeka]

6. I have heard the Sergeant of Arms has no authoritiy off of the capitol grounds.

Onenote beat me to it! Thanks Onenote.

[Pepsidog]

7. Under Bush people got away with ignoring Congress. Nothings going to change regrettably.

[watoos]

8. The Barr justice Department is not going to enforce

Contempt of Congress.
Impeachment is the only option

[watoos]

9. The Barr justice Department

Will not enforce contempt of Congress

[corbettkroehler]

11. I Wish That Were Enough

If the people who were in contempt by refusing a subpoena entered the Capitol grounds, this approach might work. Otherwise, it's up to the DOJ, run by a man who finds Congress as a whole contemptible.