Undecideds will break for...?

[The Vorlon]

There is a slim sliver of the electorate that pollsters call "The Good Citizens"

These people are weakly engaged to the political process, tend to be either independents or very softly aligned with one party, and are only marginally engaged.

They typically represent 4 or 5% of the folks who actually vote on election day, because they DO vote pretty reliably (That is why pollster call them "The Good Citizens", because "Good Citizens" vote)

They do tend to break fairly heavy to one side or the other, but it varies which way they break.  Most of them make up their mind very late in the process, often the last weekend.

You hear political folks speak of "The breeze" where things shift suddenly by a couple points right at the end... The "Good Citizens" are that breeze...

in 1980 they went massively for Reagan
In 1984 they went massively for Reagan
In 1988 they went more or less for Bush #1
in 1992 they broke for Clinton
In 1996 they broke for Dole, not that it actually mattered.
In 2000 they broke for Gore
In 2004 they more or less split.
In 2008 they modestly broke for McCain.

No real pattern as to HOW they break between the parties or the incumbent versus challenger.

HINT !

If the election is VERY close right to the end (it likely will be) trust the polls that use multi question likely voter screens that measure enthusiasm AND past vote behavior over those the use simpler screens based on interest and engagement - Typically the multi-question screens will perform a bit better.