The U.S. Moon, with its strengthening trine to Mars, and as the dispositor of Mercury and the Sun, suggests that the people collectively have the last say in what goes on in this country. The fourth house Moon symbolizes the foundations of the country, foundations which are driven toward security needs, but in an equitable way that considers the relative burden among the socio-economic classes. 

Transiting Saturn through the Aquarian fourth house has consistently brought organized movements toward socialism. In the past century, Saturn has visited this house four times, and each episode corresponded to government efforts to institutionalize solutions to recognized social imbalances. 

The pattern repeated under Kennedy and LBJ thirty years later. The Civil Rights movement began in earnest in 1962 with James Meredith becoming the first black student to attend the University of Mississippi, accompanied by 3000 federal troops to put down riots. Rachel Carson published Silent Spring, which detailed toxic pollution through corporate irresponsibility, and kicked off the environmental movement. Lyndon Johnson initiated a War on Poverty program and the momentous Civil Rights Act in 1964 as Saturn completed its passage through Aquarius. 

The fourth time Saturn crossed over the U.S. nadir was under Clinton's stewardship of the ship of state. Saturn was conjunct the U.S. Moon at the same time transiting Pluto was squaring the Moon, so the intense emotional conflicts aroused by this combination stressed some of the most volatile equal rights issues imaginable. How to deal with homosexuals in the military was Clinton's leading issue upon assuming office, and this was during the most exact contacts of transiting Pluto and Saturn to the U.S. Moon. Other unresolved issues from this era included the rights of the unborn, women's and minority rights (again), and the right of every American to a health insurance policy.
The U.S. Moon in the 4th house
The U.S. Moon plays a decisive role in American politics, especially in determining who gets elected President. For more on this topic, see Presidential Astrology
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"All of our people, except full-blooded Indians, are immigrants, or descendants of immigrants, including even those who came here on the Mayflower."  
                                                    -- Franklin D. Roosevelt
The U.S. has 16° Aquarius on the Imum Coeli, the beginning of the fourth house. And in the 4th house is the Moon, located at 25° Aquarius. 
Cancer is on the ninth house cusp, and with the exception of Native Americans, our people are all immigrants, a ninth house meaning. The ninth house also governs religion, law, and higher education. Americans' indomitable demand for equality and justice are part and parcel of the Aquarian vibration, but the house where these virtues are expressed is through the legal system, a ninth house affair. 

With the Moon in Aquarius, respect for socio-economic differences, as well as religious tolerance, represent the basic values embraced by the diverse peoples of America. The Aquarius Moon offers a powerful counterpoint to the more predatorial instincts of America's plutocracy. Transiting Uranus entered the U.S. fourth house at the beginning of the year 2000, as the Y2K problem electrified the nation.
These two degrees and their midpoint represent critical activation zones in domestic conditions, which is the natural meaning of the fourth house. The Moon describes the American people, and in any horoscope selected for July 4, 1776 the Moon will be in Aquarius. Only in the Scorpio Rising chart is the Moon in the fourth house, and by associating the house with Cancer on its cusp, the astrologer will see what affairs concern the people the most. 
Transiting Saturn first entered the U.S. fourth house this century in March 1904, and edged back and forth toward the Moon over the next year. This period saw the vilification of Standard Oil Co., filthy meat packing practices, and the torturous labor conditions in sweatshop industries. Theodore Roosevelt surprised his conservative business constituency by taking this public outrage to heart. He became known as a Trust-Buster, and proposed legislation which became the Food and Drug Purification Act, and established the FDA. The I.W.W. (the Industrial Workers of the World, or "Wobblies") was founded in June 1905, a union group which aggressively promoted putting working class people in possession of the economic power. Eugene Debs was a leading speaker during this time, and headed up the Socialist Party. Mother Mary Jones was a feisty, 75 year old woman speaking out on women's rights.

The socialist tone of Saturn in Aquarius once again flared loudly when Franklin Roosevelt came to power thirty years later. The New Deal was a comprehensive approach to ending the Great Depression through a variety of government programs to assist the downtrodden. More legislation was proposed and passed during FDR's first 100 days than ever before or since, as the bulk of his socialist agenda was completed under the escort of transiting Saturn entering the U.S. fourth house, and over the next year as
Saturn approached the natal Moon. The clear geopolitical emphasis when transiting Saturn enters Aquarius is on domestic issues, and this is entirely due to America's Aquarian nadir and Moon.

Territorial expansion can also be correlated to the Moon. The 1803 Louisiana Purchase virtually doubled the size of the United States as transiting Neptune in Scorpio squared the Moon. Forty years later Neptune was passing through the fourth house when the next greatest territorial acquisitions occurred with the ceding of the Northwest Territory by Great Britain, and the war with Mexico adding most of the Southwest, including Texas and California. 

Neptune passing through America's fourth house inspired westward expansion under the philosophy of Manifest Destiny, and the birth of the Mormon and the spiritualist movements also began during the 1840s as both Saturn and Neptune alined with the U.S. Moon. 

Oil was discovered in Pennsylvania, and gold was discovered in California, both spawning feverish rushes toward immense riches. This was when the American dream was born. Immense wealth was within grasp of ordinary citizens, and the western territorial expansion allowed anyone and everyone the space and resources for a personal domain. 
Transits to the U.S. Moon in March 1846
With transiting Neptune in the U.S. fourth house now, multiculturalism becomes a key buzzword. Ethnic diversity in American communities gives moral strength, although in many areas, and in particular across the southern frontier with Mexico, the issue of illegal immigration will likely become heated under this transit. Natally, with its Moon in Aquarius, the United States is emotionally rooted in social equality and justice. Wherever the feeling or appearance of social inequality or injustice is witnessed, Neptune here by transit urges the call for resolution.
Hay House - Helping People Improve the Quality of their Lives
This chart segment on the left shows the transits to the U.S. horoscope in May 2009, as the Moon, Jupiter, Chiron, and Neptune form a quadruple conjunction to the U.S. Moon. 
There's much more on the U.S. Scorpio Rising chart at NeptuneCafe:

Why Scorpio?
Pluto, the Ruling Planet
Sun in 9th House
Fist of God Formation
Leo Midheaven
The Eighth House   
Major Transits 

Major activation of the U.S. Moon often corresponds to severe weather events, and other natural and manmade catastrophes that strongly affect domestic well-being. In 1993, transiting Pluto's square to the Moon coincided with the Flood of the Century, as months of rainfall finally caused the Mississippi River to spill over across the American heartland. Previously, the record flood (also the Mississippi) was in August 1926 through April 1927, when transiting Neptune was opposite the Moon. Mount St. Helens exploded suddenly in May 1980 when transiting Uranus squared the Moon. Most major hurricanes, aeronautical accidents, earthquakes, urban riots, environmental disasters, and terrorist acts can generally be traced to the dynamic activation of the U.S. nadir or Moon.
The Mt St Helens volcano unexpectedly exploded on May 18, 1980 as transiting Uranus at 23 degrees Scorpio was squaring the U.S. Moon (orb 2 degrees)

re: USA Moon - Do you consider the Moon in the USA chart to be Void of Course? I hadn't noticed this until I read this blog where the writer uses the Sibly chart, but the same would be true (by most traditional rules) in the Scorpio chart, too.

A. This is a common argument to justify using some other date for the national horoscope. No, I don't consider the Moon to be void of course, and for several reasons: 1) the v/c rule is meant to be applied to horary charts, not geopolitical or national horoscopes. 2) So using traditional aspects, the Moon is trine Mars. Using the so-called minor aspects, the Moon is also quincunx Mercury and Neptune, and these connections form a Yod. When considering the 8th harmonic aspects, the Moon is also part of a Fist of God formation, meaning its trioctile (sesquiquadrate or 135 degree aspect) both the Sun and Saturn. This is a very dynamic formation, and can be said to dominate the chart. 3) When considering the main four asteroids, the Moon is trine Juno, square Vesta, and applying to a conjunction with Pallas in Aquarius, a very powerful connection that reinforces democratic principles. And the Moon is sextile Chiron. So you see it has a network of aspects around the chart, including being the focal point of two major configurations.