O Nell, sweet Nell, if thou dost love thy lord,
Banish the canker of ambitious thoughts!
And may that hour when I imagine ill
Against my king and nephew, virtuous Henry,
Be my last breathing in this mortal world!
(1.2.17–21)

Gloucester addresses these words to the Duchess, who has just talked about the possibility of her husband becoming king. After all, since Henry doesn’t yet have an heir, Gloucester, as Lord Protector, would be next in line for the throne. Demonstrating his honor and loyalty to the Crown, Gloucester chides his wife for her ambition, which implicitly entails the treason of wishing the king harm. But even though he instructs his wife to “banish the canker of ambitious thoughts,” the Duchess does no such thing. She responds by recounting a dream she had in which she had become queen, and she later proceeds to hire occultists to help her figure out how to make her dream a reality. Her ambition is ultimately what leads both to her own banishment and her husband’s murder.

Not all these lords do vex me half so much
As that proud dame, the Lord Protector’s wife.
She sweeps it through the court with troops of ladies
More like an empress than Duke Humphrey’s wife.
Strangers in court do take her for the queen.
. . .
Contemptuous base-born callet as she is,
She vaunted ’mongst her minions t’ other day
The very train of her worst-wearing gown
Was better worth than all my father’s lands,
Till Suffolk gave two dukedoms for his daughter.
(1.3.78–82, 86–90)

Margaret directs these words to Suffolk, explaining how irritating she finds the Duchess’s ambitious pretensions. Despite being the Lord Protector’s wife, she comports herself in such a way that visitors to the court mistake her for the queen. Margaret is clearly envious of this attention, as suggested in her complaint about the richness of the Duchess’s wardrobe. According to her exaggerated account, the materials for the train of just one of the Duchess’s gowns costs more than her father’s two dukedoms. In short, the Duchess’s ambition is an irritant that gets in the way of Margaret’s own ambition.

Now will I dam up this thy yawning mouth
For swallowing the treasure of the realm.
Thy lips that kissed the queen shall sweep the ground,
And thou that smiledst at good Duke Humphrey’s death
Against the senseless winds shall grin in vain,
Who in contempt shall hiss at thee again.
And wedded be thou to the hags of hell
For daring to affy a mighty lord
Unto the daughter of a worthless king,
Having neither subject, wealth, nor diadem.
By devilish policy art thou grown great,
And like ambitious Sulla, overgorged
With gobbets of thy mother’s bleeding heart.
(4.1.73–85)

In the opening scene of act 4, Suffolk is captured at sea while attempting to cross the English Channel to the land of his exile: France. When the Captain of the crew that has captured Suffolk learn of his identity, he unleashes these words of contempt. Everyone in England knows that Suffolk is the man who brokered the marriage between Henry and Margaret, which entailed the loss of the greater part of Normandy. He is therefore popularly despised as the one guilty of “swallowing the treasure of the realm.” Significantly, the Captain attributes Suffolk’s action to his political ambition, which has made him like the Roman dictator Lucius Cornelius Sulla, who infamously made use of state-sanctioned murder. The grotesque image of Suffolk having stuffed himself “with gobbets of [his] mother’s bleeding heart” reveals the Captain’s disgust for ambitious politicians.