NEWS
If There Are Witnesses, the Senate Can Compel Them
A snip:
The Senate is fully capable, as half of a co-equal branch of government, to enforce it subpoenas and it can look to its sergeant-at-arms to carry out arrests and imprisonment, if necessary. Since 1821, the Supreme Court has recognized the “inherent” authority of Congress to arrest and detain recalcitrant witnesses. During the Teapot Dome scandal investigation in 1927, the Supreme Court approved of the Senate’s power to have a deputy of the sergeant-at-arms arrest the former attorney general’s brother in Cincinnati when he refused to comply with a Senate subpoena.
The article has an anti-Trump slant (since there's a presupposition that they would find a credible witness against him) but obviously this power works both ways.
Sauce, which has a lot of historical information: https://thebulwark.com/if-there-are-witnesses-the-senate-can-compel-them/