In the American version too, that's the protagonist's role - the Majority Whip. In practice, in both the American and British systems, the Whip's actual power springs not from blackmail but from the more prosaic threat to withhold party support for a candidate's reelection.
What makes the British Whips (and party discipline in general) so much more powerful is that in the UK, candidates are almost completely dependent on their party for campaign financing. By contrast, in the US a candidate usually gets campaign donations directly from supporters, so a competitor from the same party supported by the party establishment is less likely to win. This is why, for example, the Tea Party in the US took the form that it did (insurgent candidates competing in primaries against the establishment's choice), whereas in the British system equivalent grassroots insurgencies are all-or-nothing affairs that target the central decision-making bodies and leadership of the party (think Jeremy Corbyn).
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In the American version too, that's the protagonist's role - the Majority Whip. In practice, in both the American and British systems, the Whip's actual power springs not from blackmail but from the more prosaic threat to withhold party support for a candidate's reelection.
What makes the British Whips (and party discipline in general) so much more powerful is that in the UK, candidates are almost completely dependent on their party for campaign financing. By contrast, in the US a candidate usually gets campaign donations directly from supporters, so a competitor from the same party supported by the party establishment is less likely to win. This is why, for example, the Tea Party in the US took the form that it did (insurgent candidates competing in primaries against the establishment's choice), whereas in the British system equivalent grassroots insurgencies are all-or-nothing affairs that target the central decision-making bodies and leadership of the party (think Jeremy Corbyn).