By mid-1925, Kamenev and Zinoviev saw that they had been outmaneuvered by Stalin.
Stalin had used the desire to beat Trotsky to fill the party bureaucracy with his own supporters.
In order to remove Zinoviev and Kamenev from the race, Stalin formed a new alliance with Bukharin in support of the NEP.
The debate over the NEP came to a had at the 14th Party Congress in December 1925.
When Lenin had established the NEP in 1921, he made it clear it was a "temporary deviation" from orthodox Marxist ideology.
However, Lenin never indicated how long the NEP was going to last.
There was disagreement about the precise timing to end the NEP.
In 1925 and 1926, Stalin and Bukharin argued that the NEP should be allowed to continue for a few more years whereas Zinoviev, Kamenev and Trotsky argued that it should be ended immediately.
The NEP was popular and Stalin now had full control at Party Congresses, so the party retained the NEP in 1925.
In response to the party retaining the NEP, Kamenev, Zinoviev and Trotsky came together to form the "United Opposition", arguing against the NEP and in favour of "Permanent Revolution".
The United Opposition was an uneasy and ineffective alliance as Kamenev and Zinoviev had bitterly attacked Trotsky in 1924 and 1925 and were accused of hypocrisy.
The United Opposition had to be constantly wary of the accusation of factionalism for disagreeing with decision made at Party Congresses.
The United Opposition put forward their views at a meeting of the Communist Party Central Committee in 1926 but were defeated.
They continued to work in secret and eventually made an appeal to the workers of Moscow to go on strike in opposition of government policy.
The United Opposition were removed from their position in power and were replaced in the Politburo by men loyal to Stalin.
In 1927, Zinoviev and Kamenev were allowed to retain their membership of the party after renouncing their "Trotskyite" views but Trotsky himself refused to abandon his principles and was exile to Alma-Ata in Central Asia.
Still refusing to abandon his opposition to Stalin, Trotsky was eventually exiled out of the USSR in 1929.