Shift in the Electorate's Makeup Tightens the Presidential Contest (POLL) It's a tale of two electorates in the ABC News/Washington Post tracking poll.

 -- It’s a tale of two electorates in the ABC News/Washington Post tracking poll, with shifts in intended turnout moving a large advantage for Hillary Clinton a week ago to a far tighter 2016 presidential race today.

From a 50-38 percent Clinton lead over Donald Trump in the tracking poll’s first four days, Oct. 20-23, it’s a 47-45 percent contest in the latest results. The movement has been in Trump’s favor, +7, while the -3 in Clinton’s support is not significant, given the sample size.

See PDF with full results here.

Changes in the poll’s latest four nights compared with the previous four are not mainly about people shifting in their candidate preference, but about changes in who’s intending to vote. Among those results in this poll, produced for ABC by Langer Research Associates:

• As Trump’s controversies last week and the week before move further into the rearview mirror, Republicans are expressing greater likelihood to participate: Eighty-one percent of registered Republicans now are likely voters, up from 75 percent a week ago.

• In one example, there are 6 points more Republicans and GOP-leaning independents showing up in the ranks of non-college white women. This group was broadly for Trump a few weeks ago, then less so; it’s now back, favoring him by 59-29 percent.

• Loosely affiliated or reluctant Clinton supporters look less likely to vote, perhaps given their sense she can win without them -- a supposition that looks less reliable today.

• Vote preferences also are part of the mix. At its lowest early this week, 82 percent of Republicans supported Trump. It’s 86 percent now. And his share of Republicans and GOP-leaning independents has gained 6 points, from 78 to 84 percent.

Trump, meanwhile, has gone from a 6-point deficit to a 16-point advantage among independents, with more Republican-leaners in their ranks.

Among other examples of partisan shifts in turnout, the share of white likely voters who are Democrats or lean that way is down by 5 points. The share of white women who are Republicans or GOP leaners is +6 points, and leaned Democrats are down 7 points in this group. And the share of 18- to 29-year-olds who are Republicans, or lean that way, is +6, though still low, while leaned Democrats age 18-29 are -9 points.

Many of these results are not statistically significant taken alone, given the sample sizes -- but these small shifts add to the larger trends.

Another way to cut the data is to take all eight waves of tracking, with interviews among 2,303 likely voters, a robust sample size; that produces a 48-42 percent contest, similar to the average in ABC/Post polls since July. But doing so sets aside the dynamics of the past week.

That said, the dynamics can continue to shift. While preferences in recent past elections have been stable, there are previous examples of wild rides. Most notable is 1992, when, among many gyrations, Bill Clinton went from an 11-point lead to a 3-point gap in six days late in the race -- a shift much like his wife is experiencing in her contest, 24 years later.

Methodology

This ABC News/Washington Post poll was conducted by landline and cellular telephone Oct. 24-27, 2016, in English and Spanish, among a random national sample of 1,148 likely voters. Results have a margin of sampling error of 3 points, including the design effect. Partisan divisions are 37-29-29 percent, Democrats-Republicans-independents.

Q5-6 were asked Oct. 25-27 among 956 likely voters; those results have a 3.5-point error margin.

The survey was produced for ABC News by Langer Research Associates of New York, N.Y., with sampling, data collection and tabulation by Abt-SRBI of New York, N.Y. See details on the survey’s methodology here.