WASHINGTON (Reuters) – President Joe Biden is willing to negotiate with opposition Republicans on U.S. border security in an effort to secure more aid for Ukraine, but not to being dictated to by an extreme wing of the party, a senior aide said on Thursday. “He is open to negotiate. What he is not open to (is) being handed an ultimatum by an extreme faction of the other party,” White House deputy national security adviser Jon Finer told the Aspen Security Forum conference in Washington. A bill to provide new security assistance for Ukraine and Israel was blocked in the U.S. Senate on Wednesday…