Senate Majority Leader Mitch McConnell recently moved to vote to open the immigration debate in the Senate. As quoted from [this article by CNN](https://edition.cnn.com/2018/02/09/politics/mcconnell-immigration-debate/index.html), he chose an unrelated bill to be used for the debate.

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> McConnell moved on the Senate floor to vote to open debate on the bill Monday evening. The bill McConnell chose was unrelated to immigration after he had said he planned to use a separate bill for the debate.
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The Senate subsequently [voted 97–1](https://www.senate.gov/legislative/LIS/roll_call_lists/roll_call_vote_cfm.cfm?congress=115&session=2&vote=00032) to invoke cloture on the motion to proceed to consideration.

From what I understand, the bill is [H.R. 2579 — Broader Options for Americans Act](https://www.congress.gov/bill/115th-congress/house-bill/2579), which was passed in the House last year.

Questions:

* As it is stated that H.R. 2579 is used as a ["vehicle for the immigration bill"](https://twitter.com/senategopfloor/status/963187680791203840), how does this exactly work? How is this particular bill chosen?
* It is mentioned that using this bill will allow Senators to ["build a bill from scratch on the Senate floor"](https://www.nytimes.com/2018/02/12/us/politics/senate-immigration-debate.html), however, why is an existing bill used to start the immigration debate? Can't a new *blank* bill be introduced instead?
* What will happen to the [existing text](https://www.congress.gov/bill/115th-congress/house-bill/2579/text/eh?) in the bill that was passed by the House? Will the existing text be removed via an amendment or will the immigration-related provisions just simply be added on to the existing text in the bill?