Both Boris and Trump were born in New York - Boris in June 1964 and Trump in June 1946. This is an easy early talking point between them, and in practice tends to give a sense of belonging to the same "family background". The small difference of two years in their ages imitates the common age differential between siblings.
Looking at the elemental balance of earth, air, fire and water in both charts, each has a lack of one element, suggesting that in order to find balance in their life, they will unconsciously seek to bring the "missing" element into their life, either through choosing friends with that elemental make-up, or through hobbies and activities. Throughout history the importance of elements was known - Galen had classified herbs into hot, cold, dry or damp, using combinations of each to specifically define a herb's medicinal potential; the four "humours" - phlegmatic (water), choleric (fire), sanguine (air), and melancholic (earth), have been used and alluded to in Jung's "four functions" of thinking (air), feeling (water), sensation (earth) and intuition (fire). Trump, with the exception of a Taurus (fixed earth) sign on his midheaven, has no planets in earth in his chart. Boris does - Jupiter in Taurus, and a Uranus/Pluto conjunction in Virgo. What Boris does not have is planets in fire signs (although his Moon in Scorpio might sometimes be mistaken as "fiery"). Trump has good fire, with Ascendant and Mars in Leo and Moon in Sagittarius. Each, therefore, will be naturally attracted towards the other, feeling comfortable, even relaxed, in each other's company.
Both individuals were born with their Sun in the sign of Gemini (mutable air). Mythology tells us about Castor and Pollux, the twins. It is said of Gemini that they are always looking for their "twin" or "soulmate". Well, if that is true, then Trump and Boris have found it - perhaps not their "twin" but someone who can think as they do (Gemini is an air sign, ruling all attributes of the mind), with similar goals - again encouraging an easy connection.
Both men being Geminis, interconnections to their ruling planet - Mercury (planet of communication, mind, facts, curiosity, business, siblings, and yes, mischief) will be important. Uranus connections to Mercury always stir up the mental process in any relationship, and Uranus in both charts connects with Mercury in the other chart. A "double whammy" so to speak, which underlines the ease with which these two statesmen are able to communicate, as well as trigger off and expand the thinking in the other. A useful connection when needing to find ways around world challenges, as well as making for interesting communication.
There is also a "double whammy" between Mercury and the North Node (loosely, a point relating to relationships and future destiny) between both charts. Boris has North Node at 2 degrees of Cancer which sits on Trump's Mercury at 8 degrees of Cancer, and Boris' Mercury at 19 degrees of Gemini sits on Trump's North Node at 20 degrees of Gemini. Destined to be brothers? Destined to do business together?
The pull of destiny is strong in both charts. Both have their Sun conjunct the North Node - Trump in the 10th house of vocation/profession/public image, and Boris in the 9th, elevated, close to the Gauquelin position (a point research showed significant to the vocation of a person). It seems that both are currently fulfilling at least part of their destiny.
Trump is known to be unpredictable, irregular in his behaviour, and ultra spontaneous - well, what would one expect of a Sun conjunct Uranus? But let us remember that Uranus is the planet that gets rid of old patterns, old ways, a planet that can destroy in an instant when the time has come for a new era, new ideas, new methods, new beginnings. Uranus does not take prisoners. In Trump's chart, Uranus is in a very tight trine to Jupiter - exacerbating the potential disruptive energy of Uranus. In Boris' chart, Uranus is conjunct Pluto (both in Virgo) opposite to Saturn in Pisces. A mutable opposition. A see-saw which pulls forwards one minute and backwards the next. Somewhat uncertain, somewhat irregular, somewhat spontaneous at times, in spite of the Saturn suggestion of a "brake" it (Saturn) sits in the potentially chaotic sign of Pisces. Not a very reliable "brake" to the Uranus energy then, allowing the overall impression of the opposition to be that of unpredictability. Which is perhaps why so many people are thinking that Boris is the UK's Trump (or "trump card" perhaps?).
It does seem that if ever they were destined to meet, then they would become buddies. The couple of difficult aspects between the charts (Mars square Mars, and Trump's Saturn square Boris' Moon) possibly serve to keep a healthy competitive spirit alive in the relationship.