Voters in five north-eastern US states will cast ballots in a series of primaries that could cement the leads of presidential front-runners Hillary Clinton and Donald Trump.
Democrat Mrs Clinton and Republican Trump hold sizeable leads in all five contests, according to recent polling.
Trump’s rivals have already shifted focus away from the north-east.
This pact of allegiance between the two has been attacked by Trump, a New York businessman, as a sign of weakness and desperation.
Connecticut, Delaware, Maryland, Pennsylvania and Rhode Island will hold primaries on Tuesday, reports the BBC.
In the Republican race, the candidates are focused on blocking Trump from gaining 1,237 delegates and forcing a contested convention this July in Cleveland.
That would mean party delegates – Republican officials and activists – choose the nominee.
The hope of a contested convention is keeping Kasich and Cruz in the race. Both candidates have no chance of securing the nomination outright.
Meanwhile, Democrat Bernie Sanders is pushing hard for a win in Rhode Island, where Mrs Clinton’s lead is slimmer. He is also hoping for an upset in working-class Pennsylvania.
However, after Tuesday’s results, it is unlikely Sanders will be able to overcome Mrs Clinton’s lead to become the Democratic nominee for president.
