First, with a Democratic Party that is united in opposing Trump, highlighting any division among Democrats is useful for Republicans. So last month, Senate Republicans forced a vote on a measure that allows state governments to sever ties with companies who support the boycott, divestment and sanctions (BDS) movement against the Israeli government. (Basically, BDS calls for companies and governments to suspend economic relations with the Israeli government.) The Senate vote almost perfectly split the Democrats, with 25 Democrats voting for the measure (backing the pro-Israeli-government position) and 22 voting against it, including 2020 candidates Cory Booker, Kirsten Gillibrand, Kamala Harris, Bernie Sanders and Elizabeth Warren. (Many Democrats, such as Sanders, don’t support BDS but argue the anti-BDS bills violate free speech rights.)
Second, casting Omar and some Democrats as anti-Semitic gives the Republicans a way to change the political debate on race and identity, which has been dominated for nearly four years by Democrats (and others) casting Trump as racist. The Omar controversy is a rare opportunity for Republicans to cast Democrats as insufficiently concerned about a minority group — and they are taking full advantage.