In each of the sentences below, faulty punctuation confuses the syntactical organization. Discussions and revisions follow each problematic sentence.
1. Documentation, such as white papers, that support model choices, data analysis and other similar assertions, will be necessary to support the elections made.
This sentence includes one parenthetical phrase (“such as white papers”), but it’s punctuated as if another, longer one is embedded after it. However, the segment of the sentence between that phrase and “will be necessary . . .” is not parenthetical, so no comma is necessary before will: “Documentation, such as white papers, that support model choices, data analysis and other similar assertions will be necessary to support the elections made.”
2. Presumptive Democratic presidential nominee, Hillary Clinton, faces consistent fire from people who oppose her policy positions, including Republican nominee, Donald Trump, and many others.
There’s a subtle distinction between an appositive (a word or phrase equivalent in meaning with an adjacent word or phrase) and a simple description. The phrases preceding the names in this sentence are descriptions; simply precede each with the and they become appositives, which are set off parenthetically. But as written, this sentence requires only one comma—the one separating the subordinate clause (beginning with “as does” from the main clause): “Presumptive Democratic presidential nominee Hillary Clinton faces consistent fire from people who oppose her policy positions, including Republican nominee Donald Trump and many others.”
3. Raucous protesters and supporters of Donald Trump violently confronted each other in California leading to twenty arrests as the Republican presidential contender brought his campaign to conservative Orange County.
The subordinate clause in this sentence, beginning with “as the Republican presidential contender,” must be set off by a comma, but an additional comma is required before the parenthetical phrase “leading to twenty arrests.” The second comma does double duty closing off the parenthetical phrase and setting off the subordinate clause from the main clause: “Raucous protesters and supporters of Donald Trump violently confronted each other in California, leading to twenty arrests, as the Republican presidential contender brought his campaign to conservative Orange County.” (The second comma is required because the arrests occurred after, not concurrent with, Trump’s arrival.)
I see the first example differently. Since the verb in the phrase “that support” is plural, it was clearly meant to match up with the phrase “white papers” and not with the singular subject “documentation.” Therefore, the comma after “papers” should be removed, not the comma after “will,” with the following result: “Documentation, such as white papers that support model choices, data analysis and other similar assertions, will be necessary to support the elections made.” However, it might have been better to reorder the sentence: “It will be necessary to support the elections made with documentation, such as white papers that support model choices, data analysis and other similar assertions.”
David Bennett said it better than I could have.